Apparatus and method for transmitting and receiving of cyclic shift parameter for supporting orthogonality in MIMO environment

ABSTRACT

A method includes: determining a Cyclic Shift (CS) parameter that implicitly indicates an orthogonality allocation rule and orthogonality-related information, by determining a multiple access state of a User Equipment (UE), and transmitting the determined CS parameter to the UE, wherein the orthogonality-related information includes an Orthogonal Cover Code indicated by the CS parameter, the orthogonality allocation rule is determined as a uniform scheme or a non-uniform scheme according to the CS parameter, determining the CS parameter by which the non-uniform scheme is applied if the UE is in a Single User Multiple Input Multiple Output state, and determining the CS parameter by which the uniform scheme is applied if the UE is in a Multiple User Multiple Input Multiple Output state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/611,852, filed on Feb. 2, 2015, which is a continuation of U.S.patent application Ser. No. 13/961,380, filed on Aug. 7, 2013, now U.S.Pat. No. 8,964,520, which is a continuation of U.S. patent applicationSer. No. 13/099,500, filed May 3, 2011, and now issued as U.S. Pat. No.8,531,939, and claims priority from and the benefit under 35 U.S.C. §119of a Korean Patent Application No. 10-2010-0041403, filed on May 3,2010, each of which is hereby incorporated by reference for all purposesas if fully set forth herein.

BACKGROUND

1. Field

Embodiments of the present invention relate to a wireless communicationsystem, and more particularly, to an apparatus and a method fortransmitting and receiving a cyclic shift parameter for supportingorthogonality in a Multiple Input Multiple Output (MIMO) environment.

2. Discussion of the Background

With the development of communication systems, a wide variety ofwireless terminals are being used by consumers, such as businesscompanies and individuals.

Current mobile communication systems, such as 3GPP (3rd GenerationPartnership Project), LTE (Long Term Evolution), and LTE-A (LTEAdvanced), may bring forth the development of technology for ahigh-speed large-capacity communication system, which can transmit orreceive various data, such as images and wireless data, and thus beyondthe capability of mainly providing a voice service, and can furthertransmit a large capacity of data in a wired communication network.Moreover, the mobile communication systems are being used with a propererror detection scheme, which can minimize the reduction of informationloss and improve the system transmission efficiency, thereby improvingthe system performance.

Further, in various communication systems, various Reference Signals(RSs) are used to provide information on a communication environment,etc. to counterpart devices through an uplink or a downlink.

For example, in a Long Term Evolution (LTE) system, which is an evolvedsystem for mobile communication, a User Equipment (UE) transmits anUplink Demodulation Reference Signal (UL DM-RS) as a reference signal ineach slot in order to obtain channel information for demodulation of adata channel at the time of uplink transmission. Further, a soundingreference signal is transmitted, as a channel estimation referencesignal indicating the channel state of the UE, to a base station(eNodeB) transceiver, and a Cell-specific Reference Signal (CRS) istransmitted at each sub-frame in order to obtain channel information atthe time of downlink transmission.

The reference signals as described above may be generated andtransmitted by a UE if they are uplink reference signals and aregenerated and transmitted by a base station (eNodeB) transceiver if theyare downlink reference signals.

Further, in the case of an uplink, reference signals are generated bygenerating a plurality of sequences through complex dimensional phaseshifting using a predetermined cyclic shift.

However, there has been a recent demand for the use of more extendedreference signals or sequences, in order to secure the flexibility ofcommunication systems, etc.

SUMMARY

Exemplary embodiments of the present invention provide an apparatus anda method for transmitting and receiving a cyclic shift parameter forsupporting orthogonality in a Multiple Input Multiple Output (MIMO)environment. Additional features of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention discloses a method fortransmitting a Cyclic Shift (CS) parameter, comprising determining a CSparameter which implicitly indicates an orthogonality allocation ruleand orthogonality-related information, by determining a multiple accessstate of one or more User Equipments (UEs), and transmitting thedetermined CS parameter to the one o—r more UEs, wherein theorthogonality-related information comprises an Orthogonal Cover Code(OCC) indicated by the CS parameter, the orthogonality allocation ruleis determined as a uniform scheme or a non-uniform scheme according to aset with at least one element to which the CS parameter belongs, if thenon-uniform scheme is applied as the orthogonality rule, determining theat least one element as the CS parameter of the UE if the UE is in anSU-MIMO (Single User Multiple Input Multiple Output) state, and if theuniform scheme is applied as the orthogonality rule, determining the atleast one element as the CS parameter of the UE if the UE is in anMU-MIMO (Multiple User Multiple Input Multiple Output) state.

An exemplary embodiment of the present invention provides a method fortransmitting a Cyclic Shift (CS) parameter to a User Equipment (UE),which generates and transmits reference signals for N layers (N is aninteger), the method comprising determining a CS parameter whichimplicitly indicates an Orthogonal Cover Code (OCC) used for generationof a reference signal for each layer, and transmitting the determined CSparameter to the UE, wherein the CS parameter is an element of a firstset or a second set, an intersection between the first set and thesecond set is an empty set, and one element of the first set isdetermined as the CS parameter if a first OCC is identically allocatedto a first layer and a second layer and another OCC different from thefirst OCC is identically allocated to a third layer and a fourth layer,and one element of the second set is determined as the CS parameter ifone OCC is identically allocated to all the N layers.

An exemplary embodiment of the present invention provides a method fortransmitting reference signals by a User Equipment (UE), which generatesand transmits reference signals for N layers (N is an integer), themethod comprising calculating a Cyclic Shift (CS) parameter value for afirst layer from control information including a CS parameter receivedfrom an eNodeB, calculating a CS parameter value for each of otherlayers if the other layers are used in addition to the first layer,calculating an Orthogonal Cover Code (OCC) for the first layer from theCS parameter, calculating an OCC for each of the other layers if theother layers are used in addition to the first layer, generating areference signal for the first layer by using the CS parameter value andthe OCC for the first layer, generating a reference signal for each ofthe other layers by using a CS parameter value and an OCC for each ofthe other layers if the other layers are used in addition to the firstlayer, and transmitting the generated reference signal to the eNodeB,wherein the CS parameter is an element of a first set or a second set,an intersection between the first set and the second set is an emptyset, and an OCC of a second layer is equal to an OCC of a first layerwhile OCCs of a third layer and a fourth layer are not equal to the OCCof the first layer if the CS parameter is an element of the first set,and one OCC is identically allocated to all the N layers if the CSparameter is an element of the second set.

An exemplary embodiment of the present invention provides a eNodeBapparatus to transmit a Cyclic Shift (CS) parameter to a User Equipment(UE), which generates and transmits reference signals for N layers (N isan integer), the eNodeB apparatus comprising a CS parameter determiningunit to determine a CS parameter which implicitly indicates anOrthogonal Cover Code (OCC) used for generation of a reference signalfor each layer, a signal generating unit to generate a signal fortransmitting control information including the determined CS parameterto the UE, and a transceiving unit to transmit the signal to the UE andto receive a reference signal from the UE, wherein the CS parameterdetermined by the CS parameter determining unit is an element of a firstset or a second set, an intersection between the first set and thesecond set is an empty set, and one element of the first set isdetermined as the CS parameter if a first OCC is identically allocatedto a first layer and a second layer and another OCC different from thefirst OCC is identically allocated to a third layer and a fourth layer,and one element of the second set is determined as the CS parameter ifone OCC is identically allocated to all the N layers.

An exemplary embodiment of the present invention provides a UserEquipment (UE) apparatus, which generates and transmits referencesignals for N layers (N is an integer), the UE apparatus comprising areceiving unit to receive control information that comprises a CyclicShift (CS) parameter from an eNodeB, a CS parameter extracting unit tocalculate a CS parameter value for a first layer from the controlinformation including the CS parameter, and to calculate a CS parametervalue for each of other layers if the other layers are used in additionto the first layer, an orthogonality-related information calculatingunit to calculate orthogonality-related information for the first layerfrom the CS parameter, and to calculate orthogonality-relatedinformation for each of the other layers if the other layers are used inaddition to the first layer, a reference signal generating unit togenerate a reference signal for the first layer by using theorthogonality-related information for the first layer and the CSparameter value for the first layer, and to generate a reference signalfor each of the other layers by using orthogonality-related informationfor each of the other layers and a CS parameter value for each of theother layers if the other layers are used in addition to the firstlayer, and a transmitting unit to transmit the generated referencesignal to the eNodeB, wherein the CS parameter is an element of a firstset or a second set, an intersection between the first set and thesecond set is an empty set, and an Orthogonal Cover Code (OCC) of asecond layer is equal to an OCC of a first layer while OCCs of a thirdlayer and a fourth layer are not equal to the OCC of the first layer ifthe CS parameter is an element of the first set, and one OCC isidentically allocated to all the N layers if the CS parameter is anelement of the second set.

An exemplary embodiment of the present invention provides a method of aUser Equipment (UE), which generates and transmits reference signals forN layers (N is an integer), in a system, the method comprising receivingcontrol information including a Cyclic Shift (CS) parameter from aneNodeB, calculating a CS parameter value of a first layer according tothe CS parameter included in the control information, and determining anOrthogonal Cover Code (OCC) and a CS parameter value for each layer byusing the calculated CS parameter value of the first layer and anequation in consideration of a maximum of four layers, which is definedby determination of the CS parameter value for each layer (if thecalculated CS parameter value is one of 0, 3, 6, and 9) {n_(DMRS) ⁽²⁾ ofthe 1st layer, n_(DMRS) ⁽²⁾ of the 2nd layer, n_(DMRS) ⁽²⁾ of the 3rdlayer, n_(DMRS) ⁽²⁾ of the 4th layer}={n_(DMRS) ⁽²⁾, (n_(DMRS) ⁽²⁾+6)mod12, (n_(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9))mod 12} determination ofthe OCC for each layer (if the calculated CS parameter value is one of0, 3, 6, and 9) {n_(DMRS) ^(OCC) of the 1st layer, n_(DMRS) ^(OCC) ofthe 2nd layer, n_(DMRS) ^(OCC) of the 3rd layer, n_(DMRS) ^(OCC) of the4th layer}={n_(DMRS) ^(OCC), n_(DMRS) ^(OCC), 1−n_(DMRS) ^(OCC),1−n_(DMRS) ^(OCC)} determination of the CS parameter value for eachlayer (if the calculated CS parameter value is one of 2, 4, 8, and 10){n_(DMRS) ⁽²⁾ of the 1st layer, n_(DMRS) ⁽²⁾ of the 2nd layer, n_(DMRS)⁽²⁾ of the 3rd layer, n_(DMRS) ⁽²⁾ of the 4th layer}={n_(DMRS) ⁽²⁾,(n_(DMRS) ⁽²⁾+6)mod 12, (n_(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}determination of the OCC for each layer (if the calculated CS parametervalue is one of 2, 4, 8, and 10) {n_(DMRS) ^(OCC) of the 1st layer,n_(DMRS) ^(OCC) of the 2nd layer, n_(DMRS) ^(OCC) of the 3rd layer,n_(DMRS) ^(OCC) of the 4th layer}={n_(DMRS) ^(OCC), n_(DMRS) ^(OCC),n_(DMRS) ^(OCC), n_(DMRS) ^(OCC)}, wherein n_(DMRS) ⁽²⁾ indicates a CSparameter value of each layer, and n_(DMRS) ^(OCC) indicates an OCCindex for each layer, which is defined by n_(DMRS) ^(OCC)=0→[+1, +1],n_(DMRS) ^(OCC)=1→[+1, −1].

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block diagram illustrating a wireless communication systemaccording to an exemplary embodiment.

FIG. 2 illustrates structures of a sub-frame and a time slot accordingto an exemplary embodiment.

FIG. 3 is a flowchart illustrating a process of generating a DM-RSsequence by a UE in an LTE environment according to an exemplaryembodiment.

FIG. 4 illustrates an orthogonality allocation rule according to anexemplary embodiment.

FIG. 5 is a flowchart illustrating a process of setting and transmittingcontrol information to a UE by an eNodeB according to an exemplaryembodiment.

FIG. 6 is a flowchart illustrating a process in which a UE infers an OCCand orthogonality allocation rule from control information transmittedby an eNodeB and sets the OCC and orthogonality allocation ruleaccording to an exemplary embodiment.

FIG. 7 is a flowchart illustrating a process in which a UE obtains anOCC by selecting an orthogonality allocation rule from controlinformation transmitted by an eNodeB according to an exemplaryembodiment.

FIG. 8 is a flowchart illustrating a process in which a UE in an MU-MIMOenvironment obtains an OCC by selecting an orthogonality allocation rulefrom control information transmitted by an eNodeB according to anexemplary embodiment.

FIG. 9 is a flowchart illustrating a process in which an eNodeBimplicitly provides an orthogonality allocation rule to a UE accordingto an exemplary embodiment.

FIG. 10 is a flowchart illustrating a process in which a UE in anMU-MIMO environment calculates an OCC value by selecting anorthogonality allocation rule from control information transmitted froman eNodeB according to an exemplary embodiment.

FIG. 11 is a block diagram of an apparatus for transmitting a CSparameter indicating the orthogonality according to an exemplaryembodiment.

FIG. 12 is a block diagram of an apparatus for receiving a CS parameterindicating the orthogonality and transmitting a reference signalsatisfying the orthogonality according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Exemplary embodiments now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsare shown. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth therein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of this disclosure to those skilled in the art.Various changes, modifications, and equivalents of the systems,apparatuses, and/or methods described herein will likely suggestthemselves to those of ordinary skill in the art. Elements, features,and structures are denoted by the same reference numerals throughout thedrawings and the detailed description, and the size and proportions ofsome elements may be exaggerated in the drawings for clarity andconvenience.

The present disclosure is directed to a technology for transmitting andreceiving a cyclic shift parameter which also implicitly indicateinformation relating to the orthogonality in a MIMO environment.

Also, the present disclosure is directed to a technology fortransmitting and receiving a cyclic shift parameter, to allow thecreation of a reference signal without a separate transmission ofinformation relating to the orthogonality.

FIG. 1 is a block diagram illustrating a wireless communication systemaccording to an exemplary embodiment.

Wireless communication systems are widely arranged in order to providevarious communication services, such as voice, packet data, etc.

Referring to FIG. 1, a wireless communication system includes a UE (UserEquipment) 10 and a BS (Base Station) 20. The UE 10 and the BS 20 mayemploy a technology of generating an extended reference signal forchannel estimation.

The UE 10 may refer to a user terminal in a wireless communication, andmay including a UE in WCDMA, LTE, HSPA (High Speed Packet Access), MS(Mobile Station), UT (User Terminal), SS (Subscriber Station), wirelessdevice and an MS (Mobile Station) in GSM (Global System for MobileCommunication), and the like.

The UE 10 and the BS 20 are not limited to specifically expressed termsor words and may be two transmitting and receiving agents used forimplementation of the technology or technical idea described herein.Further, in the following discussion, the terms “terminal”, “userterminal”, and “UE” are used as having the same meaning, and the terms“base station” and “eNodeB (evolved Node-B)” are used as having the samemeaning.

Some examples of various multiple access schemes, include CDMA (CodeDivision Multiple Access), TDMA (Time Division Multiple Access), FDMA(Frequency Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA, that canbe applied to the wireless communication system.

For the uplink transmission and the downlink transmission, it ispossible to use either a TDD (Time Division Duplex) scheme usingdifferent times for transmission or an FDD (Frequency Division Duplex)scheme using different frequencies for transmission.

Embodiments of the present invention can be applied to resourceallocation in the asynchronous wireless communication, which may be aLTE (Long Term Evolution) and the LTE-A (LTE-advanced) through the GSM,the WCDMA, and the HSPA. Further, the embodiments may be applied toresource allocation in the synchronous wireless communication, which maybe the CDMA, the CDMA-2000, and the UMB. The present invention shall notbe restrictively construed based on a particular wireless communicationfield and shall be construed to include all technical fields to whichthe concept of the present invention can be applied.

The wireless communication system, to which embodiments of the presentinvention are applied, can support uplink and/or downlink HARQ, and mayuse a Channel Quality Indicator (CQI) for link adaptation. Further,different schemes may be used for the downlink transmission and uplinktransmission. For example, an OFDMA (Orthogonal Frequency DivisionMultiple Access) scheme may be used for the downlink while an SC-FDMA(Single Carrier-Frequency Division Multiple Access) scheme is used forthe uplink.

Radio interface protocol layers between a UE and a network may beclassified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the Open SystemInterconnection (OSI)model widely known in the communication system, anda physical layer belonging to the first layer provides an informationtransfer service using a physical channel.

FIG. 2 illustrates structures of a sub-frame and a time slot accordingto an exemplary embodiment.

Referring to FIG. 2, one radio frame or wireless frame includes 10sub-frames 210, and one sub-frame includes two slots 202 and 203. Thebasic unit of data transmission is the sub-frame, and downlink or uplinkscheduling is performed for each sub-frame. One slot may includemultiple OFDM (Orthogonal Frequency Division Multiplexing) symbols inthe time domain and one or more sub-carriers in the frequency domain.Also, one slot may include 7 or 6 OFDM symbols.

For example, if a sub-frame includes two time slots, each time slot mayinclude 7 or 6 symbols in the time domain and 12 sub-carriers in thefrequency domain. A time-frequency area defined as including one slotalong the time axis and 12 sub-carriers along the frequency axis may becalled a Resource Block (RB), without limiting the present inventionthereto.

In a 3^(rd) Generation Partnership Project (3GPP) LTE system, thetransmission time of a frame is divided into Transmission Time Intervals(TTIs) each having duration of 1 ms. The terms “TTI” and “sub-frame” mayhave the same meaning, and one frame may a length of 10 ms and mayinclude 10 TTIs.

Reference numeral 202 indicates a time slot having a structure accordingto an embodiment of the present invention. As described above, the TTIis a basic transmission unit, and one TTI includes two time slots 202and 203 having the same length, with each time slot having duration of0.5 ms. The time slot includes 7 or 6 Long Blocks (LBs) 211, each ofwhich corresponds to a symbol. The LBs 211 are separated from each otherby Cyclic Prefixes (CPs) 212. In summary, one TTI or sub-frame mayinclude 14 or 12 LB symbols. However, the present disclosure is notlimited to the frame, sub-frame, or time-slot structure as describedabove.

In the LTE communication system, which is one of the current wirelesscommunication schemes, reference signals defined for the uplink includea Demodulation Reference Signal (DMRS or DM-RS) and a Sounding ReferenceSignal (SRS), reference signals defined for the downlink include aCell-specific Reference Signal (CRS), a Multicast/Broadcast over SingleFrequency Network (MBSFN) reference signal, and a UE-specific referencesignal.

Specifically, in a wireless communication system, a UE transmits anuplink Demodulation Reference Signal (UL DMRS or UL DM-RS) in each slotin order to obtain channel information for demodulation of a datachannel at the time uplink transmission. In the case of UL DM-RS relatedto a Physical Uplink Shared Channel (PUSCH), the reference signal istransmitted for one symbol in each slot. In the case of UL DM-RS relatedto a Physical Uplink Control Channel (PUCCH), the reference signal istransmitted for a maximum of three symbols in each slot. In this event,the mapped DM-RS sequence is configured in consideration of the CyclicShift (CS) and the base sequence r _(u,v)(n). In the case of LTE system,the DM-RS sequence may be configured for one layer.

FIG. 3 is a flowchart illustrating a process of generating a DM-RSsequence by a UE in an LTE environment according to an exemplaryembodiment.

$\begin{matrix}{{{r_{u,v}^{(\alpha)}(n)} = {{\mathbb{e}}^{j\;\alpha\; n}{{\overset{\_}{r}}_{u,v}(n)}}},\left\{ \begin{matrix}{0 \leq n \leq M_{sc}^{RS}} \\{M_{sc}^{RS} = {m\; N_{sc}^{RB}}} \\{1 \leq m \leq N_{RB}^{\max,{UL}}} \\M_{sc}^{RS}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, r_(u,v) ^((α))(n) indicates a Reference Signal (RS)sequence, a indicates a Cyclic Shift (CS), r _(u,v)(n) indicates a basesequence, and M_(sc) ^(RS) indicates the number of sub-carriersallocated for the UL DM-RS sequence along the frequency axis. Equation 1shows an example in which a Reference Signal (RS) sequence is calculatedby using a Cyclic Shift (CS) a and a base sequence r _(u,v)(n). First,for the UL DM-RS sequence, a base sequence, that may be based on azadoff-chu sequence, is generated (step S310). The base sequence becomesdifferent based on the group number u, the base sequence number v withinthe group, and the length n of the sequence. However, base sequences ofUL DM-RS s occupying the same frequency bandwidth at the same slot timeand in the same base station (or cell or eNodeB) may be the same.

In the meantime, the Cyclic Shift (CS) α can be obtained through acalculation defined by Equation 2 below.α=2πn _(cs)/12n _(cs)=(n _(DMRS) ⁽¹⁾ +n _(DMRS) ⁽²⁾ +n _(PRS)(n _(s)))mod 12n _(PRS)(n _(s))=Σ_(t=0) ⁷ c(8N _(symb) ^(UL) ·n _(s)+i)·2^(i)  [Equation 2]

In order to obtain α, it is necessary to obtain the value of n_(DMRS)⁽¹⁾, n_(DMRS) ⁽²⁾, and n_(PRS)(n_(s)) for n_(cs).

n_(DMRS) ⁽¹⁾ has a value determined by the value of cyclic shiftparameter given by a higher layer for n_(DMRS) ⁽¹⁾ shown in Table 1below. Therefore, n_(DMRS) ⁽¹⁾ can be calculated as shown in Table 1below (step S320).

TABLE 1 n_(DMRS) ⁽¹⁾ cyclicShift n_(DMRS) ⁽¹⁾ 0 0 1 2 2 3 3 4 4 6 5 8 69 7 10

n_(PRS)(n_(s)) can be obtained through a calculation defined by Equation2 (step S320), and a pseudo random sequence c(i) may have acell-specific value.

n_(DMRS) ⁽²⁾ is calculated by the cyclic shift in the DMRS field in themost recent DCI format 0 as shown in Table 2 below. Thus, n_(DMRS) ⁽²⁾is determined by the value of the cyclic shift parameter given by ahigher layer for n_(DMRS) ⁽²⁾. In step S330, the UE receives a 3 bitscyclic shift parameter for value of n_(DMRS) ⁽²⁾, which has beenscheduled and determined by a higher signaling layer, for example, RRC(Radio Resource Control) signaling, from an eNodeB, in which a 3 bitscyclic shift parameter may be carried by the Cyclic Shift (CS) field ofthe DCI format 0 as shown in Table 2 below. The transmitted 3 bitscyclic shift parameter in CS field may be mapped for cyclic shiftparameter value n_(DMRS) ⁽²⁾ as shown in Table 2 below, so that n_(DMRS)⁽²⁾ can be calculated (steps S330 and S340).

TABLE 2 n_(DMRS) ⁽²⁾ CS in DCI format 0 n_(DMRS) ⁽²⁾ 000 0 001 6 010 3011 4 100 2 101 8 110 10 111 9

Then, n_(cs) and α are calculated based on the values obtained in stepS320 to S340 (step S350). The parameters n_(DMRS) ⁽¹⁾ and n_(PRS)(n_(s))in n_(cs) for calculating α vary according to the eNodeB (or cell) andthe slot time. However, they are fixed values in the same eNodeB (orcell) and the same slot time. Therefore, n_(cs) may actually depends onthe parameter value of n_(DMRS) ⁽²⁾. That is, the n_(DMRS) ⁽²⁾ is theparameter value actually scheduled and transmitted to each UE by ahigher signaling layer through an eNodeB, and α, which is the CS valueof the UL DM-RS, depends on n_(DMRS) ⁽²⁾.

Further, by Equation 1 using the base sequence of step S310 and the α(CS value) of step S350, the DM-RS sequence is generated (step S360).

The DM-RS sequence generated by Equation 1 is mapped to a correspondingsymbol of each slot by a Resource Element (RE) mapper (step S370). Inthe case of DM-RS relating to the PUSCH, the symbol corresponds to thefourth symbol among the seven symbols of each slot if a normal CP isused and corresponds to the third symbol among the seven symbols of eachslot if an extended CP is used. In the case of DM-RS relating to thePUCCH, the corresponding symbol may include a maximum of three symbolsin each slot, the number and locations of corresponding symbols dependon the type of CP and the format of PUCCH as shown in Table 3 below.

TABLE 3 Symbol locations in slot depending on CP type and PUCCH formatSymbol locations in slot PUCCH format Normal CP Extended CP 1, 1a, 1b 2,3, 4 2, 3 2 1, 5 3 2a, 2b 1, 5 N/A

If the mapping has been completed, an SC FDMA generator generates anSC-FDMA symbol from an RE, to which the DM-RS sequence has been mapped,and then transmits the generated DM-RS signal to the eNodeB (S380).

The LTE-Advanced (LTE-A) system has a maximum of four antennas that aresupported for the uplink, which requires discriminative DM-RS sequencemapping for a maximum of four layers. To this end, the base sequence mayhave different CS values, to thereby maintain the orthogonality.

Further, there is a method of adding an OCC (Orthogonal Cover Code) foreach slot, which has been proposed in order to further guarantee theorthogonality between layers in SU-MIMO (Single-User Multiple InputMultiple Output) and MU-MIMO (Multiple-User Multiple Input MultipleOutput), or in order to discriminate multiple UEs in MU-MIMO.

The OCC may be configured as shown in Table 4 below.

TABLE 4 Configuration of OCC n_(occ) OCC 0 {+1, +1} 1 {+1, −1}

In the case of the conventional LTE using only one layer, a CS valuescheduled and determined by a higher signaling layer is signaled to theUE as a value of 3 bits. However, the LTE-A system should provide a CSvalue and OCC so that many layers and the UE can have the orthogonalityto each other. For example, in the case of using a maximum of fourlayers, it is necessary to apply the CS and OCC to the maximum of fourlayers, so as to guarantee the orthogonality.

Therefore, the eNodeB transfers information on n_(occ) of 1 bit, whichindicates the OCC, to the UE, so as to guarantee the orthogonalitybetween UEs or layers in the mapping of the DM-RS sequence by using thisinformation. Thus, in order to transfer n_(occ) to the UE, the eNodeBmay transmit n_(occ) by itself to the UE through direct 1 bit signaling.However, in the case of LTE-A differently from the LTE, the addition of1 bit signaling would require the addition of 1 bit to each ComponentCarrier (CC) in each sub-frame for transmission, which may causeadditional overhead. Moreover, differently from the 3 bits signalingusing the DCI format 0 in the conventional LTE, the LTE-A would require4 bits including the additional 1 bit, which requires configuration ofanother DCI format different from that of the LTE. Therefore, it isnecessary to enable the UE to use an OCC without separate 1 bitsignaling.

In the LTE system, it is may not be necessary to simultaneously take theSU-MIMO and MU-MIMO environments into consideration. However, in theLTE-A system, it may be necessary to simultaneously satisfy optimized CSvalue and OCC allocation in order to discriminate multiple UEs in theMU-MIMO and each layer in the SU-MIMO. Especially, it may be necessaryfor the UE to generate a reference signal by allocating the OCC and theCS without the additional signaling as described above.

The present disclosure presents a method and an apparatus for allocatingan OCC and a CS value in each layer of an UL DM-RS. Further, the presentdisclosure provides a method and an apparatus, which allows theallocation of different CS values and different OCCs according towhether the access state of the UE is the SU-MIMO or the MU-MIMO, sothat the OCC can be used to discriminate each layer in the SU-MIMO andto discriminate between multiple UEs in the MU-MIMO. Especially, if a CSvalue of the first layer determined at a higher signaling layer is givento a UE through an eNodeB, the UE can recognize CS values of otherlayers and the OCC of each layer from the given value without anyadditional signaling.

FIG. 4 illustrates an orthogonality allocation rule according to anexemplary embodiment.

The orthogonality allocation rule refers to a rule applied in allocatinginformation relating to the orthogonality of each layer. The informationrelating to the orthogonality may be information to indicate theorthogonal sequence used for generation reference signal. As describedabove with reference to Table 4, n_(occ), which indicates the OCC or theconfiguration of the OCC, may be an example of the information relatingto the orthogonality.

The rule shown in FIG. 4 corresponds to a rule relating to the scheme inwhich the information relating to the orthogonality is set for eachlayer. In FIG. 4, n_(occ), i.e. OCC index, is employed as an example,wherein the OCC index may have two values (0 or 1).

The orthogonality allocation rule includes a uniform scheme and anon-uniform scheme. The uniform scheme refers to a scheme in whichorthogonality-related information for a particular layer is identicallyallocated to the other layers. The uniform scheme may be employed inorder to provide the orthogonality to each UE, for example, it may beemployed in the case of the MU-MIMO. The case 410 corresponds to anexample of the uniform scheme, wherein the OCC index n_(occ) of thefirst layer is allocated without a change to the N layers.

The non-uniform scheme refers to a scheme in which the same informationas the orthogonality-related information for a particular layer isallocated to some layers while information different from theorthogonality-related information for a particular layer is allocated tothe other layers. The non-uniform scheme may be employed in order toprovide the orthogonality to each layer, for example, it may be employedin the case of the SU-MIMO.

The non-uniform scheme may include an alternating scheme and a divisionscheme. The case 420 corresponds to an example of the alternatingscheme, wherein the OCC index n_(occ) is allocated to the layers inevery other turn among the sequentially arranged 1st, 2nd, . . . , Nthlayers, that is, the OCC index n_(occ) and another index (such as1-n_(occ)) are alternately allocated to the 1st, 2nd, . . . , Nthlayers. The case 430 corresponds to an example of the division scheme,wherein the 1st, 2nd, . . . , Nth layers are divided into two groups,and the OCC index nocc is allocated to one group while another OCC index(1-nocc) is allocated to the other group. By using the orthogonalityallocation rule as described above, it is possible to allocate differentCS values and different OCCs according to whether the access state ofthe UE is the SU-MIMO or the MU-MIMO.

A separate signaling of information indicating the orthogonalityallocation rule may increase the quantity of transmitted/received data.Therefore, it may be necessary to implement an implicit scheme so thatthe UE can select the orthogonality allocation rule without a separatesignaling. Now, a method of providing orthogonality-related informationwithout a separate signaling and a method of implicitly providing anorthogonality allocation rule will be discussed.

First, a process of providing orthogonality-related information to a UEwithout a separate signaling by an eNodeB will be discussed. During thisprocess, the UE may implicitly receive orthogonality-related informationand/or an orthogonality allocation rule.

FIG. 5 is a flowchart illustrating a process of setting and transmittingcontrol information to a UE by an eNodeB according to an exemplaryembodiment.

FIG. 5 shows a process in which an eNodeB determines and transmits acyclic shift parameter to a UE so that the UE can infer an OCC, that is,the UE can estimate information relating to the orthogonality.

During the process, the eNodeB determines the multiple access state ofone or more UEs, determines a cyclic shift parameter for obtaininginformation relating to the orthogonality based on the determinedmultiple access state, and transmits the determined cyclic shiftparameter to the UE. This process will be described now in more detail.

The eNodeB identifies the number of UEs or the number of antennas (orlayers) of each UE (step S510). This identification is followed by adetermination of whether the UE corresponds to the SU-MIMO or theMU-MIMO (step S520). As a result of the determination (step S520), ifthe multiple access state of the UE is the SU-MIMO, the eNodeBdetermines whether the UE can identify that the UE is in the SU-MIMOstate (step S522). The UE can either directly identify by itself thatthe UE is in the SU-MIMO state or indirectly infer that the UE is in theSU-MIMO state, from the state information of the network, such assequence hopping of a reference signal.

If the UE can identify that the UE is in the SU-MIMO state, the eNodeBperforms step S530. The case in which the UE can identify that the UE isin the SU-MIMO state includes a state in which the UE can identify theorthogonality allocation rule through the state of the network, andcorresponds to a case in which the UE can determine, either directly byitself or through inference from another piece of information, whetherthe current access state of the UE is an SU-MIMO state or an MU-MIMOstate. In step S530, the eNodeB determines a cyclic shift parameter tobe allocated to the UE among all allocable cyclic shift parameters, anexample of which may be n_(DMRS) ⁽²⁾.

If the UE cannot identify that the UE is in the SU-MIMO state, theeNodeB performs step S535. In step S535, the eNodeB determines a cyclicshift parameter to be allocated from a first cyclic shift parametergroup including cyclic shift parameters that can be allocated in thecase of the SU-MIMO, so that the UE can identify that the UE is in theSU-MIMO state.

If the multiple access state of the UE is the MU-MIMO, the eNodeBdetermines whether the UE can identify that the UE is in the MU-MIMOstate (step S525). The UE can either directly identify by itself thatthe UE is in the MU-MIMO state or indirectly infer that the UE is in theMU-MIMO state, from the state information of the network, such assequence hopping of a reference signal.

If the UE can identify that the UE is in the MU-MIMO state, the eNodeBperforms step S540. The case in which the UE can identify that the UE isin the MU-MIMO state includes a state in which the UE can identify theorthogonality allocation rule through the state of the network, andcorresponds to a case in which the UE can determine, either directly byitself or through inference from another piece of information, whetherthe current access state of the UE is an SU-MIMO state or an MU-MIMOstate. In step S540, for the orthogonality allocation rule, the UE canset orthogonality-related information by identifying the informationrelating to the access state.

In more detail, all cyclic shift parameters allocable to the UE can begrouped into a first set and a second set, wherein an intersectionbetween the first set and the second set is an empty set. In otherwords, a cyclic shift parameter belonging to the first set shall notbelong to the second set. Further, in order to set values of cyclicshift parameters, the first set may relate to and provide firstinformation relating to the orthogonality and the second set may relateto and provide second information relating to the orthogonality.

The case in which the number of sets is at least 2 according to anembodiment of the present invention can be applied to the case wherethere are two pieces of information relating to the orthogonality. Ifthere are N pieces of information relating to the orthogonality, thecyclic shift parameters may be grouped into N sets while each of theintersections of the N sets is an empty set. Further, according toanother embodiment of the present invention, the cyclic shift parametersmay be divided by using functions, etc. instead of using sets. Thus, itis possible to use a function of mapping a predetermined cyclic shiftparameter to first information relating to the orthogonality whilemapping another cyclic shift parameter to second information relating tothe orthogonality.

The eNodeB inserts a selected cyclic shift into control information(step S550). According to an embodiment of the present invention, theeNodeB may insert the cyclic shift into Downlink Control Information(DCI) format 0 which may be related for uplink signaling in the PhysicalDownlink Control Channel (PDCCH).

Further, the eNodeB transmits the control information to the UE (stepS560). By receiving the control information, the UE can identify theorthogonality-related information in the set including the cyclic shift.Further, if the UE has determined, either directly by itself or throughinference from another piece of information, whether the current accessstate of the UE is an SU-MIMO state or an MU-MIMO state, the UE canselect an orthogonality allocation rule and set an OCC for each layeraccording to the selected orthogonality allocation rule. In thepreviously received cyclic shift, a cyclic shift parameter may be setfor each layer.

In more detail, with respect to multiple UEs, a cyclic shift parameterfor each UE is determined in the first cyclic shift parameter group orthe second cyclic shift parameter group. Although all of the multipleUEs may receive a cyclic shift parameter determined in only one groupamong the first and second cyclic shift parameter groups, two UEs havingdifferent allocated bandwidths (or non-equal bandwidth resourceallocation) receive cyclic shift parameters determined in differentcyclic shift parameter groups. At this time, the first informationrelating to the orthogonality obtained from the first cyclic shiftparameter group is determined to be different from the secondinformation relating to the orthogonality obtained from the secondcyclic shift parameter group. Thus, since it is possible to obtain theinformation relating to the orthogonality from the cyclic shiftparameter, the first cyclic shift parameter group and the second cyclicshift parameter group should be determined in such a manner thatdifferent information (e.g. different OCCs) relating to theorthogonality can be obtained from the first cyclic shift parametergroup and the second cyclic shift parameter group. Further, it may bepossible to determine the orthogonality allocation rule from the firstcyclic shift parameter group and the second cyclic shift parametergroup.

Next, if the UE cannot identify that the UE is in the MU-MIMO state, theeNodeB performs step S545. The case in which the UE cannot identify thatthe UE is in the MU-MIMO state includes a case in which the UE cannotidentify the state of the network. Since the UE cannot identify that thecurrent access state of the UE is the SU-MIMO state or the MU-MIMOstate, the UE can identify the orthogonality allocation rule through thecyclic shift parameter. Of course, it is also possible to set theorthogonality-related information by using the cyclic shift parameter.

In more detail, all cyclic shift parameters allocable to the UE can begrouped into a first set and a second set, wherein an intersectionbetween the first set and the second set is an empty set. That is, acyclic shift parameter belonging to the first set shall not belong tothe second set. Further, in order to set values of cyclic shiftparameters, the first set may relate to and provide first informationrelating to the orthogonality and the second set may relate to andprovide second information relating to the orthogonality. Further, thesecond set is divided into a 2-1^(st) set and a 2-2^(nd) set, anintersection of which is an empty set. In step S545, in the case ofMU-MIMO, the cyclic shift parameter is included in the 2-1^(st) set orthe 2-2^(nd) set for each UE. As a result, if a cyclic shift parameterextracted from the information received by the UE is included in the2-1^(st) set or the 2-2^(nd) set, the UE can extract theorthogonality-related information from the information relating to theset and can infer an orthogonality-related rule for another layer fromthe 2-1^(st) set and the 2-2^(nd) set. For example, upon receiving thecyclic shift parameter included in the 2-1^(st) set and the 2-2^(nd)set, the UE can obtain the orthogonality allocation rule for each layerproper for the MU-MIMO in the same manner.

The case in which the number of sets (the 2-1^(st) set and the 2-2^(nd)set) is 2 according to an embodiment of the present invention can beapplied to the case where there are two pieces of information relatingto the orthogonality. If there are N pieces of information relating tothe orthogonality, the cyclic shift parameters may be grouped into Nsets while each of intersections of the N sets is an empty set. Further,the cyclic shift parameters may be divided by using functions, etc.instead of using sets. Thus, it is possible to use a function of mappinga predetermined cyclic shift parameter to first information relating tothe orthogonality while mapping another cyclic shift parameter to secondinformation relating to the orthogonality.

Two or more sets may be the sets as described below. However, thepresent disclosure is not limited to the sets described below and ischaracterized by a configuration capable of transmittingorthogonality-related information without separately transmitting theorthogonality allocation rule.

In step S540, the first UE group and the second UE group correspond toan example of two or more UEs having different allocated bandwidths (ornon-equal bandwidth resource allocation) in the MU-MIMO environment. Inother words, for the groups according to the two different allocatedbandwidths in the MU-MIMO environment, which include the first UE groupand the second UE group having the two different allocated bandwidths,the eNodeB determines cyclic shift parameters of the first cyclic shiftparameter group to be received by one or more UEs in the first UE groupand cyclic shift parameters of the second cyclic shift parameter groupto be received by one or more UEs in the second UE group. In this event,the determining is made in such a manner to make the first informationrelating to the orthogonality obtained from the first cyclic shiftparameter group be different from the second information relating to theorthogonality obtained from the second cyclic shift parameter group.

In step S545, the 2-1^(st) UE group and the 2-2^(nd) UE group correspondto an example of two or more UEs having different allocated bandwidths(or non-equal bandwidth resource allocation) in the MU-MIMO environment.In other words, for the groups according to the two different allocatedbandwidths in the MU-MIMO environment, which include the 2-1^(st) UEgroup and the 2-2^(nd) UE group having the two different allocatedbandwidths, the eNodeB determines cyclic shift parameters of the2-1^(st) cyclic shift parameter group to be received by one or more UEsin the 2-1^(st) UE group and cyclic shift parameters of the 2-2^(nd)cyclic shift parameter group to be received by one or more UEs in the2-2^(nd) UE group. In this event, the determining is made in such amanner to make the first information relating to the orthogonalityobtained from the 2-1^(st) cyclic shift parameter group be differentfrom the second information relating to the orthogonality obtained fromthe 2-2^(nd) cyclic shift parameter group.

Especially, the two UEs having different allocated bandwidths (non-equalbandwidth resource allocation) may be scheduled to necessarily receiveCS parameters for n_(DMRS) ⁽²⁾ of different CS-OCC linkage groups (inthe MU-MIMO environment, two UEs having the same allocated bandwidths(equal bandwidth resource allocation) need not be scheduled tonecessarily receive CS parameters for n_(DMRS) ⁽²⁾ of different CS-OCClinkage groups).

As described above with reference to FIG. 5, the eNodeB generates CSparameter for n_(DMRS) ⁽²⁾, which enable inference of an OCC valuewithout separate setting of the OCC value. That is, the UE may calculatea corresponding OCC value from the CS parameter for n_(DMRS) ⁽²⁾received through the DCI format, etc. and applies the calculated OCCvalue to generation of the DM-RS. There may be various processes ofcalculating the OCC value from the CS parameter for n_(DMRS) ⁽²⁾. Asnoted from Table 4, if the OCC index has a value of 0 or 1, the value ofthe CS parameter for n_(DMRS) ⁽²⁾ may be divided by 2 and a remainder ofthe division may be taken as the OCC index value. Further, as anotherexample, it is possible to take a scheme of previously linking the CSparameter for n_(DMRS) ⁽²⁾ and the OCC to each other into consideration.

The eight types of CS parameters for n_(DMRS) ⁽²⁾ values from the 3 bitsCS field of the DCI format 0 in the LTE system as shown in Table 2 maybe divided into two CS-OCC linkage groups each including four n_(DMRS)⁽²⁾ values as shown in Table 5. The CS parameter values n_(DMRS) ⁽²⁾ inone group are identically linked to one OCC index n_(DMRS) ⁽²⁾, while CSparameter values n_(DMRS) ⁽²⁾ in the other group are linked to the otherOCC index n_(DMRS) ^(OCC). Such linkage is shown in Table 5. However,the method of dividing the CS parameter values n_(DMRS) ⁽²⁾ into twogroups is not limited to the configuration and allocation as shown inTable 5. Instead, the CS parameter values n_(DMRS) ⁽²⁾ may be grouped toguarantee the maximum orthogonality through the OCC and a uniformdistribution of the DM-RS. For example, in consideration of four CSparameter values {0,3,6,9}, which are applicable in four layers of rank4, they may be grouped in a uniform and crossed manner so that the OCCindex for {0,6} has a value of 0 while the OCC index for {3,9} has avalue of 1.

In Table 5, if the n_(DMRS) ⁽²⁾ is 0, 6, 4, or 10, the OCC index is 0and the UE thus allocates [+1, +1] for the OCC value. And if then_(DMRS) ⁽²⁾ is 3, 9, 2, or 8, the OCC index is 1 and the UE thusallocates [+1, −1] for the OCC value.

TABLE 5 CS-OCC linkage rule CS parameter OCC index Cs parameter n_(DMRS)⁽²⁾ n_(DMRS) ^(OCC) CS-OCC n_(DMRS) ⁽²⁾ : n_(DMRS) ^(OCC) = linkagegroup A {0, 6, 4, 10} 0 (→[+1, +1] CS-OCC n_(DMRS) ⁽²⁾ : n_(DMRS) ^(OCC)= linkage group B {3, 9, 2, 8} 1 (→[+1, −1]

Table 5 presents an example of inference of an OCC from a CS by using agroup. Besides, the eNodeB and the UE may share information (e.g.n_(DMRS) ⁽²⁾ modulus (mod) 2) of a function having the CS value as aninput value. Of course, Table 5 may be implemented as a function.

In the case of applying the configuration shown in Table 5, if a CyclicShift (CS) value for the first layer scheduled and determined by ahigher signaling layer is given (i.e. signaled) to the UE through aneNodeB, it is possible to allocate an OCC of each layer according to apredetermined orthogonality allocation rule and a CS value of anotherlayer based on the given or signaled value.

First, a case in which the orthogonality allocation rule is anon-uniform scheme is discussed hereinafter.

The eNodeB generates a control signal, which includes DCI format 0including a 3 bits CS parameter for value of n_(DMRS) ⁽²⁾ determined foreach UE by a higher signaling layer of the system. A higher signalinglayer determines whether each UE to be scheduled will operate in anSU-MIMO or an MU-MIMO. If the UE operates in an SU-MIMO state, theeNodeB transmits a 3 bits CS parameter which indicate CS parameter value(n_(DMRS) ⁽²⁾) regardless of the CS-OCC linkage group of Table 5. Thus,in the case of the SU-MIMO, the 3 bits CS parameter for value ofn_(DMRS) ⁽²⁾ determined for each UE by a higher signaling layer of thesystem is one of the eight types of values including the CS-OCC linkagegroup A and the CS-OCC linkage group B as shown in Table 5, and theeNodeB transmits the 3 bits CS parameter for value of n_(DMRS) ⁽²⁾ toeach UE.

The eNodeB transmits the generated control information. Specifically,this 3 bits parameter may be carried by the CS field of the DCI format0.

If the corresponding UEs operate in the MU-MIMO state, the eNodeBconsiders the CS-OCC linkage groups shown in Table 5 in transmitting the3 bits CS parameter for value of n_(DMRS) ⁽²⁾. Thus, in the case of theMU-MIMO, in scheduling by a higher signaling layer of the system inorder to determine the CS parameter which indicate CS parameter value(n_(DMRS) ⁽²⁾) for each UE, UEs may be scheduled to select different CSparameter which indicate CS parameter values (n_(DMRS) ⁽²⁾) of differentCS-OCC linkage groups. Especially, two UEs having different allocatedbandwidths (non-equal bandwidth resource allocation) should be scheduledto necessarily receive CS parameters for n_(DMRS) ⁽²⁾ of differentCS-OCC linkage groups (in the MU-MIMO environment. However, in theMU-MIMO environment, two UEs having the same allocated bandwidths (orequal bandwidth resource allocation) need not be scheduled to receive CSparameters for n_(DMRS) ⁽²⁾ of different CS-OCC linkage groups). Thatis, if one UE has been scheduled to receive one of the four CSparameters for value of n_(DMRS) ⁽²⁾ of the CS-OCC linkage group A, theother UE is scheduled to receive one of the four CS parameters forn_(DMRS) ⁽²⁾ of the CS-OCC linkage group B. For example, if UE #1 hasreceived 0, which is one of the four CS parameter values n_(DMRS) ⁽²⁾ ofthe CS-OCC linkage group A, for a particular layer, UE #2 receives 3,which is one of the four CS parameter values n_(DMRS) ⁽²⁾ of the CS-OCClinkage group B, for the same layer. In this event, the two UEs in theMU-MIMO environment inevitably have different OCC indexes, so that theycan be discriminated from each other.

Next, the UE receives the 3 bits CS parameter for value of n_(DMRS) ⁽²⁾scheduled and determined by a higher signaling layer of the systemthrough the eNodeB. This 3 bits parameter may be carried by the CS fieldof the DCI format 0. As described above, this 3 bits CS parameter forvalue of n_(DMRS) ⁽²⁾ is scheduled and determined by a higher signalinglayer of the system according to whether the state of the correspondingsystem is the SU-MIMO or the MU-MIMO. The UE can know the n_(DMRS) ⁽²⁾from this 3 bits parameter as in Table 2 described above, and calculatesthe CS value α of the UL DM-RS by Equation 1 described above. In thisevent, although other parameters n_(DMRS) ⁽¹⁾ and n_(PRS)(n_(s))configuring n_(cs) are different according to the eNodeB (or cell) andthe slot time, they are fixed for the same eNodeB (or cell) and slottime. Therefore, the parameter actually scheduled and transmittedthrough the eNodeB by the higher signaling layer for a UE is n_(DMRS)⁽²⁾. As a result, the CS values α of the UL DM-RS become different.

Thus, the UE calculates the CS values α from the CS parameter for valueof n_(DMRS) ⁽²⁾ in the DCI format 0 scheduled and determined by a highersignaling layer of the system and transmitted through the eNodeB.Further, the UE calculates the OCC index n_(DMRS) ^(OCC) of the firstlayer from the received CS parameter for value of n_(DMRS) ⁽²⁾ by apredefined CS-OCC linkage rule. An example of the predefined CS-OCClinkage rule is shown in Table 5 described above. For example, if the CSparameter value n_(DMRS) ⁽²⁾ is 0, 6, 4, or 10, which correspond to theCS-OCC linkage group A in Table 5, the n_(DMRS) ^(OCC) is automaticallycalculated as 0. In contrast, if the CS parameter value n_(DMRS) ⁽²⁾ is3, 9, 2, or 8, which correspond to the CS-OCC linkage group B in Table2, the n_(DMRS) ^(OCC) is automatically calculated as 1. If the n_(DMRS)^(OCC) is 0, it may correspond to an OCC {+1, +1}. If the n_(DMRS)^(OCC) is 1, it may correspond to an OCC {+1, −1}. The mathematicalexpression and values of the parameters expressing the OCC index are notlimited as long as the meaning and contents thereof are not changed.

Next, the UE determines if there is any layer to be additionallyallocated or used further beyond the first layer. If there is anadditional layer, the UE calculates the CS values α of a correspondinglayer from the CS parameter value n_(DMRS) ⁽²⁾ of the first layer, andcalculates the OCC index n_(DMRS) ^(OCC) of the corresponding layer fromthe OCC index n_(DMRS) ^(OCC) of the first layer.

In this event, the CS allocation rule, by which the CS values α of acorresponding layer is calculated from the CS parameter value n_(DMRS)⁽²⁾ of the first layer, is the most proper method capable of reducinginter-layer interference, if the total number of layers is taken intoconsideration and the CS values allocated to the layers have distancesas large as possible.

Equation 3 below shows an example of the CS allocation rule.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layerIn SU-MIMO, n _(DMRS) ⁽²⁾ε{0,6,3,4,2,8,10,9}In MU-MIMO, n _(DMRS) ⁽²⁾ε{0,6,4,10} or n _(DMRS) ⁽²⁾ε{3,9,2,8}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12, (n _(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12} or {n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+6)mod 12, (n _(DMRS) ⁽²⁾+9)mod 12}  [Equation 3]

In Equation 3, the 1^(St) layer refers to the first layer, and the2^(nd), 3^(rd), . . . layers refer to the second, third, . . . layers.Further, rank refers to the number of layers.

In the case of rank 2 in Equation 3, the CS values of the first andsecond layers are set to have an interval of 6 (180 degrees) betweenthem so that they can be spaced as much as possible within 360 degrees.In the case of rank 3, the CS values are set to have an interval of 4(120 degrees) between them so that they can be spaced as much aspossible within 360 degrees. Further, in the case of rank 4, the CSvalues are set to have an interval of 3 (90 degrees) between them sothat they can be spaced as much as possible within 360 degrees.

Therefore, once the CS value of the first layer has been set, the CSvalues of the other layers are set to have a largest distance accordingto the rank number based on the first layer.

After the CS values of the layers are calculated, the UE calculates OCCindexes of the 2^(nd) to N^(th) layers based on the OCC of the firstlayer or the CS parameter for n_(DMRS) ⁽²⁾. As described above, the UEcalculates the OCC of the first layer through the n_(DMRS) ⁽²⁾ accordingto the scheme as shown in Table 5. Further, the OCC also may beallocated to have orthogonality. The OCCs of the second, third, . . .layers may be calculated from the OCC (i.e. value obtained from the CSparameter for n_(DMRS) ⁽²⁾) of the first layer. To this end, inconsideration of the number of all layers, if the OCC values allocatedto the layers are related to preset CS values, the CS allocation rulesecures an orthogonality as large as possible, so as to reduce theinter-layer interference as much as possible. In Equation 4 definedbelow, the n_(DMRS) ^(OCC) may be set to have different values for thefirst, second, third, and fourth layers, in order to guarantee themaximum orthogonality as in Equation 3.

Further, the CS allocation rule, by which the OCC index of acorresponding layer is calculated from the OCC index n_(DMRS) ^(OCC) ofthe first layer, is a proper method capable of reducing inter-layerinterference, if the total number of layers is taken into considerationand the OCC values allocated to the layers have the maximumorthogonality in relation to possible preset CS values. To this end,only for discriminating the layers, alternating OCC values wouldguarantee the maximum orthogonality. Thus, for example, if the OCC indexvalue of the first layer is 0, the OCC index value of the second layermay be 1, the OCC index value of the third layer may be 0, and the OCCindex value of the fourth layer may be 1. However, for discriminationbetween two UEs in the MU-MIMO, each UE should have the same OCC indexin all the layers. Thus, if UE #1 has an OCC index of 0 while UE #2 hasan OCC index of 1 in the MU-MIMO environment, UE #1 should have the OCCindex of 0 for all the layers and UE #2 should have the OCC index of 1for all the layers. In order to achieve simultaneously optimized OCCallocation in discrimination between multiple UEs in the MU-MIMO and indiscrimination of each layer in the SU-MIMO, the division schemedescribed above with reference to FIG. 4 may be taken intoconsideration. In this event, in rank 2, since the effect isinsignificant, the OCC has the same index value in the first and secondlayers while a different index value in the third and fourth layers.Equation 4 defined below shows an example of the OCC allocation rule, inwhich the OCC values allocated to the layers have the maximumorthogonality in relation to possible preset CS values, according to thenumber of layers, and which achieves simultaneously optimized OCCallocation in discrimination between multiple UEs in the MU-MIMO and indiscrimination of each layer in the SU-MIMO.n _(DMRS) ^(OCC): OCC index of the 1^(st) layern _(DMRS) ^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC), 1−n _(DMRS)^(OCC)}  [Equation 4]

Table 6 shows an example of CS parameter values and OCC indexes in thelayers configured through allocation thereof according to Equations 3and 4. In Table 6, the value scheduled and signaled by a highersignaling layer is the CS parameter for n_(DMRS) ⁽²⁾ of the first layer.In case 5 of Table 6, UE A and UE B share the same bandwidth (equalbandwidth resource allocation). In this event, UE A and UE B receive aCS parameter for n_(DMRS) ⁽²⁾ within one CS-OCC linkage group as the CSparameter value of the first layer, through which they are identified bythe cyclic shift value of the same OCC index. UE C and UE D receive a CSparameter for n_(DMRS) ⁽²⁾ within another CS-OCC linkage group differentfrom that of the UE A and UE B, through which they are identified by anOCC index different from that of the UE A and UE B.

Thus, as shown in case 5 of Table 6, the number of UEs in the MU-MIMOenvironment may be two or more. However, in this event also, two UEgroups having different bandwidths (non-equal bandwidth resourceallocation) are inevitably required in order to apply the OCC. Further,a CS parameter for n_(DMRS) ⁽²⁾ within the same CS-OCC linkage group isscheduled and transmitted as the CS parameter value of the first layerto UEs within the same group. However, between UE groups havingdifferent allocated bandwidths, CS parameter for n_(DMRS) ⁽²⁾ withindifferent CS-OCC linkage groups should be scheduled and transmitted asthe CS parameter value of the first layer to the UEs.

TABLE 6 1^(st) 2^(nd) 3^(rd) 4^(th) UL DM-RS layer layer layer layerSU-MIMO Case 1 - 2 Rank, 1 UE UE A n_(DMRS) ⁽²⁾ 0 6 n_(DMRS) ^(OCC) [+1,+1] [+1, +1] Case 2 - 3 Rank, 1 UE UE A n_(DMRS) ⁽²⁾ 0 4 8 n_(DMRS)^(OCC) [+1, +1] [+1, +1] [+1, −1] Case 3 - 4 Rank, 1 UE UE A n_(DMRS)⁽²⁾ 0 6 3 9 n_(DMRS) ^(OCC) [+1, +1] [+1, +1] [+1, −1] [+1, −1] MU-MIMOCase 4 - 2 Rank per UE A n_(DMRS) ⁽²⁾ 0 6 UE, 2 UEs n_(DMRS) ^(OCC) [+1,+1] [+1, +1] UE B n_(DMRS) ⁽²⁾ 3 9 n_(DMRS) ^(OCC) [+1, −1] [+1, −1]Case 5 - 1/2/4 Rank per UE A n_(DMRS) ⁽²⁾ 0 UE, 3 UEs n_(DMRS) ^(OCC)[+1, +1] UE B n_(DMRS) ⁽²⁾ 6 9 n_(DMRS) ^(OCC) [+1, +1] [+1, +1] UE Cn_(DMRS) ⁽²⁾ 2 5 n_(DMRS) ^(OCC) [+1, −1] [+1, −1]

If the calculation of the CS and OCC for the allocated layers has beencompleted, the UE generates a DM-RS sequence of each layer by applyingEquation 1 to the CS value α determined for each layer and the basesequence for each layer. Then, the UE multiplies the generated DM-RSsequence by a orthogonal sequence value (+1 or −1) in the OCC indexdetermined for each layer, so as to generate a final DM-RS sequence.Thus, if the OCC is [+1,+1], the value of Equation 1 is applied withoutchange to the DM-RS sequence of the first symbol (or the first slot ofone sub-frame if there is one symbol for each slot) and to the DM-RSsequence of the second symbol (or the second slot of one sub-frame ifthere is one symbol for each slot). If the OCC is [+1,−1], the value ofEquation 1 is applied without change to the DM-RS sequence of the firstsymbol (or the first slot of one sub-frame if there is one symbol foreach slot) while a value obtained by multiplying the value of Equation 1by −1 is applied to the DM-RS sequence of the second symbol (or thesecond slot of one sub-frame if there is one symbol for each slot).

The CS and OCC allocation rule described above, which achievessimultaneously optimized OCC allocation in discrimination betweenmultiple UEs in the MU-MIMO and in discrimination of each layer in theSU-MIMO, supports a rank number of 4 or less for each UE in the SU-MIMOand supports a rank number of 2 or less for each UE in the MU-MIMO. Ifthe rule can support a rank number of 4 or less for each UE in theMU-MIMO, it is possible to achieve simultaneously optimized CS and OCCallocation in discrimination between multiple UEs in the MU-MIMO and indiscrimination of each layer in the SU-MIMO, if different CS and OCCallocation rules are employed for the SU-MIMO and the MU-MIMO. Thus, fordiscriminating the layers, alternating OCC index values of the layerswould guarantee the maximum orthogonality. For example, if the OCC indexvalue of the first layer is 0, the OCC index value of the second layermay be 1, the OCC index value of the third layer may be 0, and the OCCindex value of the fourth layer may be 1. Further, for discriminationbetween two UEs in the MU-MIMO, each UE may have the same OCC index inall the layers. Thus, if UE #1 has an OCC index of 0 while UE #2 has anOCC index of 1 in the MU-MIMO environment, UE #1 should have the OCCindex of 0 for all the layers and UE #2 should have the OCC index of 1for all the layers.

In order to achieve the simultaneously optimized OCC allocation indiscrimination between multiple UEs in the MU-MIMO and in discriminationof each layer in the SU-MIMO, different CS and OCC allocation rules inthe SU-MIMO and in the MU-MIMO may be required in order to support arank number of 4 or less for each UE not only in the SU-MIMO but also inthe MU-MIMO. To this end, it may be necessary to provide an additional 1bit signaling for the SU-MIMO and the MU-MIMO or a system enabling theUE to determine by itself whether the UE is in the SU-MIMO state or theMU-MIMO state. The present disclosure has discussed implicitly differentCS and OCC allocation rules in the SU-MIMO and the MU-MIMO even withoutadditional signaling in a typical UE, which may not determine by itselfwhether the UE is in the SU-MIMO state or the MU-MIMO state. In stepS525 of FIG. 5, the eNodeB determines whether the UE can identify thatthe UE is in the MU-MIMO state. Further, even in a non-transparentsystem in which the UE can identify by itself that the UE is in theMU-MIMO state, the eNodeB performs step S540. Likewise, if the networkis characterized in that the UE is informed that the UE is in theSU-MIMO state or MU-MIMO state although the UE cannot determine byitself, for example, even if the UE can determine through a sequence orsequence group hopping, the eNodeB may perform step S540. If the UEcannot determine by itself but can be informed through a CS-OCC linkagerule, such a linkage rule can be applied.

Further, the eNodeB can be designed either for step S540 (includingS530) of FIG. 5 or for step S545 (including S535) of FIG. 5. Thus, eacheNodeB may be configured and operate either in consideration of stepsS530 and S540, which are performed if the UE can directly or indirectlydetermine whether the UE is in the SU-MIMO state or MU-MIMO state, or inconsideration of steps S535 and S545, which are performed if the UEcannot directly or indirectly determine whether the UE is in the SU-MIMOstate or MU-MIMO state. In other words, the process of FIG. 5 includestwo procedures including a determination step. If one procedure isselected according to the situation, the two procedures may be separatedwithout the determination step, and the eNodeB may be configured foronly one procedure.

FIG. 6 is a flowchart illustrating a process in which a UE infers an OCCand orthogonality allocation rule from control information transmittedby an eNodeB and sets the OCC and orthogonality allocation ruleaccording to an exemplary embodiment.

Briefly describing the process, a UE using one or more layers receives acyclic shift parameter for a first layer from an eNodeB, and calculatesinformation relating to the orthogonality with respect to the firstlayer from the received cyclic shift parameter for the first layer. Ifthere is a layer to be additionally allocated, the UE calculates acyclic shift parameter for the layer to be additionally allocated fromthe cyclic shift parameter for the first layer, and then selects anorthogonality allocation rule. Further, the UE obtainsorthogonality-related information for the additionally allocated layerby using the orthogonality allocation rule and orthogonality-relatedinformation for the first layer, generates a reference signal for thefirst layer by using the orthogonality-related information for the firstlayer and the cyclic shift parameter for the first layer, generates areference signal for the additionally allocated layer by using theorthogonality-related information for the additionally allocated layerand the cyclic shift parameter for the additionally allocated layer, andthen transmits the generated reference signal to the eNodeB.

In more detail, the UE first receives control information from theeNodeB (step S610). The control information may be information carriedby a PDCCH. Then, the UE obtains the cyclic shift parameter for thefirst layer from the control information (step S620). In the case of thePDCCH, the DCI format 0 may include the cyclic shift parameter for thefirst layer. Further, the UE obtains the orthogonality-relatedinformation for the first layer from the cyclic shift parameter for thefirst layer (step S630). An example of the orthogonality-relatedinformation for the first layer may be indication information for theOCC. It is possible to obtain the orthogonality-related information forthe first layer through a group including the cyclic shift parameter forthe first layer or a predetermined function from the cyclic shiftparameter for the first layer. Thus, the cyclic shift parameter for thefirst layer belongs to a particular cyclic shift parameter group, andthe orthogonality-related information for the first layer isorthogonality-related information relating to the particular cyclicshift parameter group to which the cyclic shift parameter for the firstlayer belongs.

The cyclic shift parameter for the first layer and theorthogonality-related information for the first layer are used togenerate the reference signal for the first layer.

Further, the UE selects an orthogonality allocation rule necessary forallocation or calculation of the orthogonality-related information forlayers (step S635). As described above with reference to FIG. 4, theorthogonality allocation rule is a rule for determining the scheme ofallocating orthogonality-related information to other layers by usingthe orthogonality-related information for the first layer. Theorthogonality allocation rule may include a uniform scheme and anon-uniform scheme. Further, the selection of the orthogonalityallocation rule may include a step in which the UE identifies thecurrent access state or infers the current access state from thesequence hopping or the sequence group hopping. Further, as anotherscheme, it is possible to select the orthogonality allocation rule toapply, through the cyclic shift parameter for the first layer. Thescheme of selecting the orthogonality allocation rule will be describedlater in more detail.

Then, the UE determines whether there is a layer to be additionallyallocated (step S640). If there is a layer to be additionally allocated,the UE obtains a cyclic shift parameter for the layer to be additionallyallocated from the cyclic shift parameter for the first layer (stepS650). Likewise, by using the selected orthogonality allocation rule andthe orthogonality-related information for the first layer, the UEobtains the orthogonality-related information for the layer to beadditionally allocated (step S660).

Further, if there is no layer to be additionally allocated, the UEgenerates reference signals for the allocated layers (step S670). Then,the UE transmits the generated reference signals to the eNodeB (stepS680). An example of the generated reference signals may be a DM-RS.

The orthogonality-related information may be information indicating anorthogonality cover code.

FIGS. 7 and 8 are flowcharts illustrating a process of allocating an OCCvalue to each layer by selecting an orthogonality allocation rule byusing sequence hopping information, and generating and transmitting areference signal by allocating a CS value to each layer.

The selection of the orthogonality allocation rule in FIGS. 7 and 8 usesdifferent CS and OCC allocation rules according to the sequence orsequence group hopping scheme. Thus, according to the hopping scheme,the DM-RS sequence may apply the SU-MIMO scheme, an equal sized Resourceallocation type MU-MIMO scheme, or a non-equal sized Resource allocationtype MU-MIMO scheme. For example, if the hopping scheme for the DM-RSsequence is “enabled” in the LTE Rel-8 system, that is, in the case ofhopping by the unit of slot, the CS and OCC allocation rule defined byEquation 5 described below is applied. This corresponds to anapplication of the SU-MIMO scheme (including the equal sized Resourceallocation type MU-MIMO scheme) as the multiple access scheme. If thehopping scheme for the DM-RS sequence is “disabled” in the LTE Rel-8system or is not the hopping by the unit of slot in the in the existingLTE Rel-8 system (e.g. hopping by the unit of sub-frame), the CS and OCCallocation rule defined by Equation 6 described below is applied. Thiscorresponds to an application of the MU-MIMO scheme (especially, thenon-equal sized Resource allocation type MU-MIMO scheme) as the multipleaccess scheme.

FIG. 7 is a flowchart illustrating a process in which a UE obtains anOCC by selecting an orthogonality allocation rule from controlinformation transmitted by an eNodeB according to an exemplaryembodiment.

The UE 701 calculates n_(PRS)(n_(s)) as in Equation 2 and n_(DMRS) ⁽¹⁾given by a higher layer as in Table 1 as cyclic shift parameter valuesnecessary for obtaining the CS values and the base sequence r _(u,v)(n)based on a zadoff-chu sequence for the UL DM-RS sequence (step S710).The base sequence has a value changing according to the group number u,the base sequence number v within the group, and the length n of thesequence. However, UL DM-RSs occupying the same frequency bandwidth atthe same slot time in the same eNodeB (or cell) have the same basesequence. As a result, the parameter actually scheduled by a highersignaling layer and transmitted through an eNodeB is n_(DMRS) ⁽²⁾, whichdetermines the CS value of the UL DM-RS.

Step S710 reflects the multiple access state or the configuration of thesystem, and may be performed either after or in combination with thevarious steps of FIG. 7.

The eNodeB generates a control signal, which includes DCI format 0including a 3 bits CS parameter for value of n_(DMRS) ⁽²⁾ determined foreach UE by a higher signaling layer of the system (step S715).Specifically, the higher signaling layer determines whether each UE tobe scheduled will operate in an SU-MIMO (including the equal sizedResource allocation type MU-MIMO) state or an MU-MIMO (including thenon-equal sized Resource allocation type MU-MIMO) state. If the UE is tooperate in an SU-MIMO (including the equal sized Resource allocationtype MU-MIMO) state, the eNodeB transmits a 3 bits CS parameter forvalue of n_(DMRS) ⁽²⁾ regardless of the CS-OCC linkage group of Table 5.Thus, in the case of the SU-MIMO, the 3 bits CS parameter for value ofn_(DMRS) ⁽²⁾ determined for each UE by the higher signaling layer of thesystem is one of the eight types of values including the values of theCS-OCC linkage group A and the CS-OCC linkage group B as shown in Table5, and the eNodeB transmits the 3 bits CS parameter for value ofn_(DMRS) ⁽²⁾ to each UE.

The eNodeB transmits the generated control information (step S720).Specifically, this 3 bits parameter may be carried by the CS field ofthe DCI format 0.

The UE calculates CS parameter value (n_(DMRS) ⁽²⁾) from the receivedcontrol information (step S725).

Thereafter, the UE calculates the CS value and the OCC value of thefirst layer, wherein the OCC can be obtained by calculating n_(cs) and αfrom the n_(DMRS) ⁽²⁾ by using Equation 2 and then calculating then_(DMRS) ^(OCC) by using the n_(DMRS) ⁽²⁾ in Table 5 (step S730). Forexample, if the n_(DMRS) ⁽²⁾ is 0, the n_(DMRS) ^(OCC) is 0 by Table 5,which may correspond to an OCC of [+1, +1]. For example, if thetransmitted CS parameter value n_(DMRS) ⁽²⁾ is 0, 6, 4, or 10, whichcorrespond to the CS-OCC linkage group A in Table 5, the n_(DMRS) ^(OCC)is automatically calculated as 0 even without receiving additionalinformation. In contrast, if the transmitted CS parameter value n_(DMRS)⁽²⁾ is 3, 9, 2, or 8, which correspond to the CS-OCC linkage group B inTable 5, the n_(DMRS) ⁽²⁾ is automatically calculated as 1 even withoutreceiving additional information. In Table 5, if the n_(DMRS) ^(OCC) is0, it may correspond to an OCC {+1, +1}. If the n_(DMRS) ^(OCC) is 1, itmay correspond to an OCC {+1, −1}. However, the mathematical expressionand values of the parameters expressing the OCC index are not limited aslong as the meaning and contents thereof are not changed.

If the CS and OCC values for the first layer have been set, the UEdetermines if there is any layer to be additionally allocated. If thereis a layer to be additionally allocated, the UE calculates the CS valuesα of the layer or layers to be additionally allocated, which may includethe 2^(nd)˜N^(th) layers, from the CS parameter for n_(DMRS) ⁽²⁾ of thefirst layer (step S735).

In this event, it is possible to apply a rule (CS allocation rule) forcalculating the CS values α of a corresponding layer from the CSparameter for n_(DMRS) ⁽²⁾ of the first layer. According to the CSallocation rule, the CS values allocated to the layers are set to havedistances as large as possible, so as to reduce the inter-layerinterference. Equation 3 shows an example of the CS allocation rule, bywhich the CS values allocated to the layers are set to have distances aslarge as possible. Equation 3 shows two representative cases as anexample of the CS allocation rule. However, the CS allocation rule isnot limited by the two cases of Equation 3 and may be configured invarious ways within the range capable of guaranteeing the orthogonalityas much as possible in each layer.

After the CS allocation is completed, it is necessary to select anorthogonality allocation rule. Therefore, the UE identifies the sequencehopping scheme (step S736). As a result of the identification, if thesequence hopping scheme is “enable” or hopping by the unit of slot, itis possible to infer that the access scheme is the SU-MIMO scheme or theequal sized Resource allocation type MU-MIMO scheme. In this event,since it is possible to allocate the OCC in order to discriminate thelayer of the UE, the non-uniform scheme, that is, the alternating schemeor the division scheme may be selected as the orthogonality allocationrule, and the OCC values of the other layers may be calculated by theselected scheme (step S737). This will be discussed by Equation 5 below.

If the sequence hopping scheme is “disable” or hopping by the unit ofsub-frame, it is possible to infer that the access scheme is the MU-MIMOscheme, more specifically, the non-equal sized Resource allocation typeMU-MIMO scheme. In this event, since it is possible to allocate the OCCin order to discriminate between the UEs, the uniform scheme may beselected as the orthogonality allocation rule so as to obtain the OCCvalues of the other layers, which are the same as the OCC value of thefirst layer (step S739). This will be discussed by Equation 6 below.

Equation 5 shows CS/OCC values of each layer by the orthogonalityallocation rule and CS allocation of the frequency hopping by the unitof slot (or activated sequence hopping). The orthogonality allocationrule in Equation 5 corresponds to a non-uniform scheme, and specificallypresents an alternating scheme.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer n _(DMRS)⁽²⁾ε{0,6,3,4,2,8,10,9}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+3)mod 12, (n _(DMRS) ⁽²⁾+6)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) }={n _(DMRS) ^(OCC), 1−n _(DMRS)^(OCC) , n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC),1−n _(DMRS) ^(OCC)}  [Equation 5]

Equation 6 shows CS/OCC values of each layer by the orthogonalityallocation rule and CS allocation of the frequency hopping by the unitof sub-frame (or inactivated sequence hopping). In Equation 6, two UEsexist and CS parameter values of the first layer to be allocated to theUEs are different values. As a result, the two UEs have different OCCvalues, which are identically applied to all the layers in the UEs.Therefore, the OCC values included in all the layers of UE A are thesame and the OCC values included in all the layers of UE B are also thesame. However, the OCC value of UE A and the OCC value of UE B aredifferent from each other, which can more clearly guarantee theorthogonality between reference signals of UE A and UE B.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layern _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Aε{0,6,4,10}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Bε{3,9,2,8}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+3)mod 12, (n _(DMRS) ⁽²⁾+6)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) ,n _(DMRS) ^(OCC)}  [Equation 6]

If the calculation of the CS and OCC for the allocated layers has beencompleted, the UE generates a DM-RS sequence of each layer by applyingthe Equations described above to the CS value α determined for eachlayer and the base sequence for each layer. Then, the UE multiplies thegenerated DM-RS sequence by a orthogonal sequence value (+1 or −1) inthe OCC index determined for each layer, so as to generate a final DM-RSsequence (step S745). For example, if Equation 5 is applied and the OCCis [+1,+1], the value of Equation 5 is applied without change to theDM-RS sequence of the first symbol (or the first slot of one sub-frameif there is one symbol for each slot) and to the DM-RS sequence of thesecond symbol (or the second slot of one sub-frame if there is onesymbol for each slot). However, if the OCC is [+1,−1], the value ofEquation 5 is applied without change to the DM-RS sequence of the firstsymbol (or the first slot of one sub-frame if there is one symbol foreach slot) while a value obtained by multiplying the value of Equation 5by −1 is applied to the DM-RS sequence of the second symbol (or thesecond slot of one sub-frame if there is one symbol for each slot).

Further, the generated DM-RS sequence is mapped to a correspondingsymbol of each slot by a resource element mapper (step S750). In thecase of DM-RS relating to the PUSCH, the symbol corresponds to thefourth symbol among the seven symbols of each slot if a normal CP isused and corresponds to the third symbol among the seven symbols of eachslot if an extended CP is used. In the case of DM-RS relating to thePUCCH, the corresponding symbol may include a maximum of three symbolsin each slot, the number and locations of corresponding symbols dependon the type of CP and the format of PUCCH as shown in Table 3 describedabove. If the mapping has been completed, an SC-FDMA generator generatesan SC-FDMA symbol from an RE, to which the DM-RS sequence has beenmapped (step S755), and then transmits the generated DM-RS signal to theeNodeB (S760).

If the hopping scheme for the DM-RS sequence is “enabled” in the LTERel-8 system, that is, in the case of hopping by the unit of slot, thelayers are allocated different OCC index values for discriminationbetween the layers. Specifically, as noted from Equation 5, alternatingvalues are allocated to the OCC indexes of the layers. That is, forexample, if the OCC index value of the first layer is 0, the OCC indexvalue of the second layer may be 1, the OCC index value of the thirdlayer may be 0, and the OCC index value of the fourth layer may be 1. Inthis event, the CS parameter for the first layer scheduled and signaledby the higher signaling layer is one of the eight types of values inTable 2. The orthogonality allocation rule of Equation 5 is thealternating scheme of the non-uniform scheme and may be modified to thedivision scheme of the non-uniform scheme as shown in Equation 7 below.In this event, the same OCC value is applied to the first two layers,and another OCC value is applied to the other two layers, so as todivide the layers by the two OCC values.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer, n _(DMRS)⁽²⁾ε{0,6,3,4,2,8,10,9}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={—n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12, (n _(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC),1−n _(DMRS) ^(OCC)}  [Equation 7]

If the hopping scheme for the DM-RS sequence is “disabled” in the LTERel-8 system or is not the hopping by the unit of slot in the in theexisting LTE Rel-8 system (e.g. hopping by the unit of sub-frame), thelayers are allocated the same OCC index while the UEs are allocateddifferent OCC indexes as in Equation 6 for discrimination between theUEs in the MU-MIMO. That is, if UE #1 has an OCC index of 0 while UE #2has an OCC index of 1 in the MU-MIMO environment, UE #1 should have theOCC index of 0 for all the layers and UE #2 should have the OCC index of1 for all the layers. In this event, the higher signaling layerschedules and transmits a 3 bits CS parameter for value of n_(DMRS) ⁽²⁾in consideration of the CS-OCC linkage group as shown in Table 5described above. That is, in the case of MU-MIMO, at the time ofscheduling in order to determine the CS parameter value n_(DMRS) ⁽²⁾ foreach UE by the system higher signaling layer, UEs may be scheduled toselect CS parameter for n_(DMRS) ⁽²⁾ of different CS-OCC linkage groups.Especially, the two UEs having different allocated bandwidths (ornon-equal bandwidth resource allocation) should be scheduled toinevitably receive CS parameters for n_(DMRS) ⁽²⁾ of different CS-OCClinkage groups (in the MU-MIMO environment, two UEs having the sameallocated bandwidths (or equal bandwidth resource allocation) need notbe scheduled to necessarily receive CS parameters for n_(DMRS) ⁽²⁾ ofdifferent CS-OCC linkage groups). In other words, if one UE is scheduledto receive one of the four CS parameters for n_(DMRS) ⁽²⁾ of CS-OCClinkage group A shown in Table 5, the other UE is scheduled to receiveone of the four CS parameters for n_(DMRS) ⁽²⁾ of CS-OCC linkage group Bshown in Table 5.

For example, if UE #1 receives 0, which is one of the four CS parametervalues n_(DMRS) ⁽²⁾ of CS-OCC linkage group A shown in Table 5, for thefirst layer, UE #2 receives 3, which is one of the four CS parametervalues n_(DMRS) ⁽²⁾ of CS-OCC linkage group B shown in Table 5, for thesame layer. In the event, two different UEs inevitably have differentOCC indexes in the MU-MIMO environment, by which they can be alwaysdiscriminated from each other. As Equation 6 is related to Equation 5,Equation 8 defined below can be applied to the MU-MIMO also in relationto Equation 7.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer, n _(DMRS)⁽²⁾ε{0,6,3,4,2,8,10,9}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Aε{0,6,4,10}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Bε{3,9,2,8}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12, (n _(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) ,n _(DMRS) ^(OCC)}  [Equation 8]

FIG. 8 is a flowchart illustrating a process in which a UE in an MU-MIMOenvironment obtains an OCC by selecting an orthogonality allocation rulefrom control information transmitted by an eNodeB according to anexemplary embodiment.

FIG. 8 shows a process in which an eNodeB 809 sets a 3 bits CS parameterand transmits control information including the CS parameter to UE #1801 belonging to the first UE group and UE #2 802 belonging to thesecond UE group. Each of the first and second UE groups may include oneor more UEs. The description with reference to FIG. 8 is based on anassumption that each of the UE groups corresponds to one UE. In thisevent, the OCC value can be obtained from the CS parameter by the UEs801 and 802 without separate signaling. The description about FIG. 8 isbased on the MU-MIMO environment, which is thus limited to theinactivated sequence hopping or the sequence hopping by the unit ofsub-frame. As a result, the orthogonality allocation rule is alsolimited to the uniform scheme.

Each of the UE #1 801 and UE #2 802 calculates n_(PRS)(n_(s)) as inEquation 2 and n_(DMRS) ⁽¹⁾ given by a higher layer as in Table 1 ascyclic shift parameter values necessary for obtaining the CS values andthe base sequence r _(u,v)(n) based on a zadoff-chu sequence for the ULDM-RS sequence (step S810 or S815). The base sequence has a valuechanging according to the group number u, the base sequence number vwithin the group, and the length n of the sequence. However, UL DM-RSsoccupying the same frequency bandwidth at the same slot time in the sameeNodeB (or cell) have the same base sequence. As a result, the parameteractually scheduled by a higher signaling layer and transmitted throughan eNodeB is CS parameter for n_(DMRS) ⁽²⁾ which determines the CS valueof the UL DM-RS.

Step S810 or S815 reflects the multiple access state or theconfiguration of the system, and may be performed either after or incombination with various steps of FIG. 8.

The eNodeB generates a control signal, which includes DCI format 0including a 3 bit CS parameters for value of n_(DMRS) ⁽²⁾ determined foreach UE by a higher signaling layer of the system (step S816).Specifically, the higher signaling layer determines whether each of UE#1 801 or UE #2 802 to be scheduled will operate in an SU-MIMO state oran MU-MIMO state. If the UE will operate in the MU-MIMO state, theeNodeB transmits 3 bits CS parameter for value of n_(DMRS) ⁽²⁾ belongingto different CS-OCC linkage groups of Table 5 to the UEs (step S816).This may cause the CS value allocation to be performed to enable the UEsto obtain different OCC values.

Now, the transmitted 3 bits CS parameters for value of n_(DMRS) ⁽²⁾ arebriefly discussed. In the case of the MU-MIMO, as the 3 bits CSparameter for value of n_(DMRS) ⁽²⁾ determined for each UE by the highersignaling layer of the system, one of the four types of values of theCS-OCC linkage group A in Table 5 is transmitted to UE #1 801 and one ofthe four types of values of the CS-OCC linkage group B in Table 5 istransmitted to UE #2 802. In more detail, in the case of MU-MIMO, at thetime of scheduling in order to determine the CS parameter for value ofn_(DMRS) ⁽²⁾ for each UE by the system higher signaling layer, the UEsmay be scheduled to select CS parameter for n_(DMRS) ⁽²⁾ of differentCS-OCC linkage group. That is, according to the CS-OCC linkage, thesystem higher signaling layer may allocate n_(DMRS) ⁽²⁾ relating to thefirst OCC to UE #1 801 and n_(DMRS) ⁽²⁾ relating to the second OCC to UE#2 802, so that UE #1 801 and UE #2 802 having received the CS parameterfor value of n_(DMRS) ⁽²⁾ can allocate different OCCs.

Especially, two UEs having different allocated bandwidths (non-equalbandwidth resource allocation) should be scheduled to inevitably receiveCS parameters for n_(DMRS) ⁽²⁾ of different CS-OCC linkage groups (inthe MU-MIMO environment, two UEs having the same allocated bandwidths(equal bandwidth resource allocation) need not be scheduled tonecessarily receive CS parameters for n_(DMRS) ⁽²⁾ of different CS-OCClinkage groups). In other words, if UE #1 801 is scheduled to receiveone of the four CS parameter values n_(DMRS) ⁽²⁾ of CS-OCC linkage groupA related to the OCC value of 0, the other UE is scheduled to receiveone of the four CS parameter values n_(DMRS) ⁽²⁾ of CS-OCC linkage groupB related to the OCC value of 1. For example, if UE #1 receives 0, whichis one of the four CS parameter values n_(DMRS) ⁽²⁾ of CS-OCC linkagegroup A, for a particular layer, UE #2 receives 3, which is one of thefour CS parameter values n_(DMRS) ⁽²⁾ of CS-OCC linkage group B, for thesame layer. In the event, two different UEs inevitably have differentOCC indexes in the MU-MIMO environment, by which they can be alwaysdiscriminated from each other. For convenience of description, FIG. 8 isbased on an assumption that 0 of the CS-OCC linkage group A relating tothe first OCC value of 0 is transmitted as the CS parameter valuen_(DMRS) ⁽²⁾ to UE #1 801, and 3 of the CS-OCC linkage group B relatingto the second OCC value of 1 is transmitted as the CS parameter valuen_(DMRS) ⁽²⁾ to UE #2 802.

The eNodeB 809 generates control information including 3 bits CSparameters for n_(DMRS) ⁽²⁾ differently set according to the UEs (stepS816), and transmits the generated control information to the UEs 801and 802 (steps S818 and S819). More specifically, this 3 bits parametermay be carried by the CS field of the DCI format 0.

Further, the transmission in steps S818 and S819 may be performed eithersequentially or with a time interval, and the generation andtransmission of the control information in step S816 may also beperformed with a time interval between UE #1 and UE #2. In addition, theprocesses performed by UE #1 and UE #2 are independent of each other, sothey are not limited by a particular sequence or simultaneous execution.Hereinafter, in spite of the independency of the two processes, theywill be described together without imposing a limitation on or givingany relation between them.

Each of UE #1 801 and UE #2 802 calculates the 3 bits CS parameter forvalue of n_(DMRS) ⁽²⁾ from the received control information (step S820or S825).

Thereafter, the UE calculates the CS value and the OCC value of thefirst layer, wherein the OCC can be obtained by calculating n_(cs) and αfrom the n_(DMRS) ⁽²⁾ by using Equation 2 and then calculating then_(DMRS) ^(OCC) by using the n_(DMRS) ⁽²⁾ in Table 5 (step S830 orS835). For example, if the n_(DMRS) ⁽²⁾ of UE #1 801 is 0, the n_(DMRS)^(OCC) is 0 by Table 5, which may correspond to the OCC of UE #1 801being [+1, +1]. Further, if the n_(DMRS) ⁽²⁾ of UE #2 802 is 3, then_(DMRS) ^(OCC) is 1 by Table 5, which may correspond to the OCC of UE#2 802 being [+1, −1].

Therefore, if the transmitted CS parameter value n_(DMRS) ⁽²⁾ is 0, 6,4, or 10, which correspond to the CS-OCC linkage group A in Table 5, UE#1 801 or UE #2 802 can automatically calculate the n_(DMRS) ^(OCC) as 0even without receiving additional information. In contrast, if thereceived CS parameter value n_(DMRS) ⁽²⁾ is 3, 9, 2, or 8, whichcorrespond to the CS-OCC linkage group B in Table 5, the n_(DMRS) ^(OCC)is automatically calculated as 1 without receiving additionalinformation. In Table 5, if the n_(DMRS) ^(OCC) is 0, it may correspondto an OCC {+1, +1}. if the n_(DMRS) ^(OCC) is 1, it may correspond to anOCC {+1, −1}. The mathematical expression and values of the parametersexpressing the OCC index are not limited as long as the meaning andcontents thereof are not changed.

In steps S830 and S835, UE #1 801 has an OCC value of [+1, +1] and UE #2802 has an OCC value of [+1, −1]. Before those steps, UE #1 801 and UE#2 802 have calculated the values of 0 and 3 as the n_(DMRS) ⁽²⁾.

If the CS and OCC values for the first layer have been set, each of theUE #1 801 and UE #2 802 determines if there is a layer to beadditionally allocated. If there is a layer to be additionallyallocated, each of the UE #1 801 and UE #2 802 calculates the CS valuesα of the layer or layers to be additionally allocated, which may includethe 2^(nd)˜N^(th) layers, from the CS parameter value n_(DMRS) ⁽²⁾ ofthe first layer (step S840 or S845).

In this event, it is possible to apply a rule (such as the CS allocationrule) for calculating the CS values α of a corresponding layer from theCS parameter value n_(DMRS) ⁽²⁾ of the first layer. According to the CSallocation rule, the CS values allocated to the layers are set to havedistances as large as possible, so as to reduce the inter-layerinterference. Equation 3 shows an example of the CS allocation rule, bywhich the CS values allocated to the layers are set to have distances aslarge as possible.

For reference, if UE #1 801 has obtained 0 as the value n_(DMRS) ⁽²⁾ andUE #2 802 has obtained 3 as the value n_(DMRS) ⁽²⁾, the n_(DMRS) ⁽²⁾ foreach layer of UE #1 801 is: i) {0, 6} for each of the first and secondlayers in the case of rank 2; ii) {0, 4, 8} for each of the first,second, and third layers in the case of rank 3; and iii) {0, 3, 6, 9} or{0, 6, 3, 9} for each of the first, second, third, and fourth layers inthe case of rank 4.

The n_(DMRS) ⁽²⁾ for each layer of UE #2 802 is: i) {3, 9} for each ofthe first and second layers in the case of rank 2; ii) {3, 7, 11} foreach of the first, second, and third layers in the case of rank 3; andiii) {3, 6, 9, 0} or {6, 3, 9, 0} for each of the first, second, third,and fourth layers in the case of rank 4. Besides Equation 3, a scheme ofsetting the layers to be spaced as far as possible may be employed.

After calculating the CS value for each layer, each of UE #1 801 and UE#2 802 determines if the sequence hopping is “disabled” or a sub-framehopping, selects the uniform scheme as the orthogonality allocationrule, and obtains the same value as the OCC value of the first layer asthe OCC index values of the second to N^(th) layers (step S850 or S855).As described above, the OCC of the first layer is calculated from the CSparameter for n_(DMRS) ⁽²⁾ according to the scheme shown in Table 5.Further, the OCC may also be allocated to have the orthogonality. TheOCCs of the second, third, . . . layers may be allocated the same valueas that of the OCC (i.e. value obtained from the n_(DMRS) ⁽²⁾) of thefirst layer. This can be performed by applying the orthogonalityallocation rule for allocation of OCCs with the orthogonality betweenUEs.

In order to guarantee the maximum orthogonality between the UEs as inEquations 6 and 8 described above with reference to FIG. 7, the samen_(DMRS) ^(OCC) is set for the first, second, third, and fourth layers.

In steps S830 and S835, UE #1 801 has obtained an OCC value of [+1, +1]by using the OCC index of 0. Further, UE #2 802 has obtained an OCCvalue of [+1, −1] by using the OCC index of 1. As a result, the OCCvalue for each layer of UE #1 801 is: i) {0, 0} for each of the firstand second layers in the case of rank 2; ii) {0, 0, 0} for each of thefirst, second, and third layers in the case of rank 3; and iii) {0, 0,0, 0} for each of the first, second, third, and fourth layers in thecase of rank 4.

The OCC value for each layer of UE #2 802 is: i) {1, 1} for each of thefirst and second layers in the case of rank 2; ii) {1, 1, 1} for each ofthe first, second, and third layers in the case of rank 3; and iii) {1,1, 1, 1} for each of the first, second, third, and fourth layers in thecase of rank 4.

If the calculation of the CS and OCC for the allocated layers has beencompleted, each of UE #1 801 and UE #2 802 generates a DM-RS sequence ofeach layer by applying Equation 1 to the CS value α determined for eachlayer and the base sequence for each layer, and multiplies the generatedDM-RS sequence by a orthogonal sequence value (+1 or −1) in the OCCindex determined for each layer, so as to generate a final DM-RSsequence (step S860 or S865). Further, the generated DM-RS sequence ismapped to a corresponding symbol of each slot by a resource elementmapper (step S870 or S875). In the case of DM-RS relating to the PUSCH,the symbol corresponds to the fourth symbol among the seven symbols ofeach slot if a normal CP is used and corresponds to the third symbolamong the seven symbols of each slot if an extended CP is used. In thecase of DM-RS relating to the PUCCH, the corresponding symbol mayinclude a maximum of three symbols in each slot, the number andlocations of corresponding symbols become different depending on thetype of CP and the format of PUCCH as shown in Table 3 described above.If the mapping has been completed, an SC-FDMA generator generates anSC-FDMA symbol from an RE, to which the DM-RS sequence has been mapped(step S755), and then transmits the generated DM-RS signal to the eNodeB(step S890 or 895).

FIGS. 7 and 8 show a process in which a UE determines a sequence hoppingscheme and selects an orthogonality allocation rule.

FIGS. 9 and 10 show a process in which an eNodeB implicitly provides anorthogonality allocation rule to a UE during the process of allocating aCS value so that the UE can infer the orthogonality allocation rule.

In the process shown in FIGS. 9 and 10, the scheme presented by Table 5is departmentalized so as to divide the CS-OCC linkage group accordingthe SU-MIMO and the MU-MIMO and to then divide the MU-MIMO CS-OCClinkage group into two groups for two UEs. An example of the division isshown in Table 7 below. In Table 9, the linkage groups are divided intoAB (including B-1 and B-2) according to the CS parameter, and the UE caninfer the OCC index for the group and can infer the orthogonalityallocation rule.

TABLE 7 CS parameter OCC index Orthogonality CS parameter n_(DMRS) ⁽²⁾n_(DMRS) ^(OCC) Allocation Rule CS-OCC linkage n_(DMRS) ⁽²⁾ ε {0, 3, 6,9} n_(DMRS) ^(OCC) = Non-uniform group A 0 (→[+1, +1] scheme CS-OCClinkage n_(DMRS) ⁽²⁾ ε {2, 4} n_(DMRS) ^(OCC) = Uniform group B-1 0(→[+1, +1] scheme CS-OCC linkage n_(DMRS) ⁽²⁾ ε {8, 10} n_(DMRS) ^(OCC)= Uniform group B-2 1 (→[+1, −1] scheme

In this method, different CS and OCC allocation rules are used accordingto the CS parameter value for the first layer. That is, the CS and OCCallocation rules become different according to whether the CS parametervalue for the first layer belongs to the CS-OCC linkage group A for theSU-MIMO or the CS-OCC linkage group B-1 or B-2 for the MU-MIMO. Forexample, if the CS parameter value for the first layer belongs to theCS-OCC linkage group (group A of Table 7) for the SU-MIMO, the CS andOCC allocation rule as defined in Equation 9 below is applied. If the CSparameter value for the first layer belongs to the CS-OCC linkage groupB-1 or B-2 for the MU-MIMO, the CS and OCC allocation rule as defined inEquation 10 below is applied.

Equation 9 shows an application in the case of the CS-OCC linkage groupA.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer n _(DMRS) ⁽²⁾ε{0,3,6,9}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+3)mod 12, (n _(DMRS) ⁽²⁾+6)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC), 1−n_(DMRS) ^(OCC) ,n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC),1−n _(DMRS) ^(OCC)}  [Equation 9]

If the CS parameter value for the first layer belongs to the CS-OCClinkage group (group A of Table 7) for the SU-MIMO, the CS and OCCallocation rule of Equation 9 is applied, wherein alternating values areallocated to the OCC indexes of the layers as shown in Equation 9.

In other words, if the OCC index value of the first layer is 0, the OCCindex value of the second layer is 1, the OCC index value of the thirdlayer is 0, and the OCC index value of the fourth layer is 1. In thisevent, the CS parameter value for the first layer scheduled and signaledby the higher signaling layer is one of the four types of valuesbelonging to the group for the SU-MIMO among the CS and OCC linkagegroups in shown in Table 9 described above.

Equation 10 below shows an application in the case of the CS-OCC linkagegroup B-1 or B-2.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer, n _(DMRS)⁽²⁾ε{2,4,8,10}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Aε{2,4}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Bε{8,10}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+3)mod 12, (n _(DMRS) ⁽²⁾+6)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) ,n _(DMRS) ^(OCC)}  [Equation 10]

If the CS parameter value for the first layer belongs to the CS-OCClinkage group (group B of Table 7) for the MU-MIMO, the layers areallocated the same OCC index while the UEs are allocated different OCCindexes as in Equation 10 for discrimination between the UEs in theMU-MIMO. Thus, if UE #1 has an OCC index of 0 while UE #2 has an OCCindex of 1 in the MU-MIMO environment, UE #1 should have the OCC indexof 0 for all the layers and UE #2 should have the OCC index of 1 for allthe layers.

In this event, the higher signaling layer schedules and transmits a 3bits CS parameter for value of n_(DMRS) ⁽²⁾ in consideration of twogroups (group B-1 or B-2) within the CS-OCC linkage group (group B ofTable 7) for the MU-MIMO as shown in Table 7 described above. Thus, inthe case of MU-MIMO, at the time of scheduling in order to determine theCS parameter value n_(DMRS) ⁽²⁾ for each UE by the higher layersignaling, UEs may be scheduled to select CS parameters for n_(DMRS) ⁽²⁾of different CS-OCC linkage groups within the CS-OCC linkage group(group B of Table 7) for the MU-MIMO. Especially, two UEs havingdifferent allocated bandwidths (or non-equal bandwidth resourceallocation) should be scheduled to inevitably receive CS parameters forn_(DMRS) ⁽²⁾ of different CS-OCC linkage groups (in the MU-MIMOenvironment, two UEs having the same allocated bandwidths (or equalbandwidth resource allocation) may not be scheduled to receive CSparameters for n_(DMRS) ⁽²⁾ of different CS-OCC linkage groups). Inother words, if one UE is scheduled to receive one of the two CSparameter values n_(DMRS) ⁽²⁾ of one CS-OCC linkage group B-1 among thetwo CS-OCC linkage groups (group B in Table 9), the other UE isscheduled to receive one of the two CS parameter values n_(DMRS) ⁽²⁾ ofthe CS-OCC linkage group B-2. For example, if UE #1 receives 4, which isone of the two CS parameter values n_(DMRS) ⁽²⁾ of CS-OCC linkage groupB-1, for the first layer, UE #2 receives 8, which is one of the two CSparameter values n_(DMRS) ⁽²⁾ of CS-OCC linkage group B-2, for the samelayer. In the event, two different UEs inevitably have different OCCindexes in the MU-MIMO environment, by which they can be alwaysdiscriminated from each other.

Equation 9 may be modified into Equation 11, wherein the same OCC indexvalue is allocated to the first two layers while another value isallocated to the other two layers. That is, Equation 9 corresponds tothe alternating scheme among the non-uniform scheme, while Equation 11corresponds to the division scheme among the non-uniform scheme in theorthogonality allocation rule. In relation with Equation 11, Equation 10may be modified into Equation 12 below.n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer n _(DMRS) ⁽²⁾ε{0,3,6,9}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12, (n _(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC), 1−n _(DMRS) ^(OCC),1−n _(DMRS) ^(OCC)}  [Equation 11]n _(DMRS) ⁽²⁾: CS parameter of the 1^(st) layer, n _(DMRS)⁽²⁾ε{2,4,8,10}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Aε{2,4}n _(DMRS) ⁽²⁾ of the 1^(st) layer for UE Bε{8,10}

1) In the case of Rank 2{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd)layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12}

2) In the case of Rank 3{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer}={n _(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+4)mod12, (n _(DMRS) ⁽²⁾+8)mod 12}

3) In the case of Rank 4{n _(DMRS) ⁽²⁾ of the 1^(st) layer, n _(DMRS) ⁽²⁾ of the 2^(nd) layer, n_(DMRS) ⁽²⁾ of the 3^(rd) layer, n _(DMRS) ⁽²⁾ of the 4^(th) layer}={n_(DMRS) ⁽²⁾, (n _(DMRS) ⁽²⁾+6)mod 12, (n _(DMRS) ⁽²⁾+3)mod 12, (n_(DMRS) ⁽²⁾+9)mod 12}n _(DMRS) ^(OCC): OCC index of the 1^(st) layer n _(DMRS)^(OCC)=0→[+1,+1], n _(DMRS) ^(OCC)=1→[+1,−1]

1) In the case of Rank 2{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

2) In the case of Rank 3{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer}={n _(DMRS) ^(OCC) , n_(DMRS) ^(OCC) , n _(DMRS) ^(OCC)}

3) In the case of Rank 4{n _(DMRS) ^(OCC) of the 1^(st) layer, n _(DMRS) ^(OCC) of the 2^(nd)layer, n _(DMRS) ^(OCC) of the 3^(rd) layer, n _(DMRS) ^(OCC) of the4^(th) layer}={n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) , n _(DMRS) ^(OCC) ,n _(DMRS) ^(OCC)}  [Equation 12]

The process of determining the linkage group to which the CS parameterbelongs is nearly similar to the processes shown in FIGS. 7 and 8.

FIG. 9 is a flowchart illustrating a process in which an eNodeBimplicitly provides an orthogonality allocation rule to a UE accordingto an exemplary embodiment.

In FIG. 9, steps S915 and S936 are different from corresponding steps ofFIG. 7 while the other steps S710, S720, S725, S730, S735, S737, S739,S745, S750, S755, and S760 are similar to corresponding steps of FIG. 9.

The eNodeB 709 generates a control signal, which includes DCI format 0including a 3 bits CS parameter for n_(DMRS) ⁽²⁾ determined for each UEby a higher signaling layer of the system, by referring to the linkagegroup presented in Table 7 (step S915). Specifically, a higher signalinglayer of the system determines whether each UE to be scheduled willoperate in an SU-MIMO (including the equal sized Resource allocationtype MU-MIMO) state or an MU-MIMO (including the non-equal sizedResource allocation type MU-MIMO) state. If the UE will operate in theSU-MIMO (including the equal sized Resource allocation type MU-MIMO)state, the eNodeB transmits a 3 bits CS parameter for n_(DMRS) ⁽²⁾included in the CS-OCC linkage group A of Table 7 (step S915). On theother hand, in the case of the MU-MIMO, from among the linkage groupsshown in Table 7 for each UE, a CS parameter value of group B-1 istransmitted to one UE while a CS parameter value of group B-2 istransmitted to the other UE. Thereafter, the process of receiving the CSparameter and inferring an OCC value by the UE is the same as that inFIG. 7.

Further, the UE determines the group to which the CS parameter belongs,from the OCC value. In the case of a CS value included in group A (thefirst linkage group) from among the linkage groups shown in Table 7, anorthogonality allocation rule of an allocating scheme or a divisionscheme, which corresponds to the non-uniform scheme of the orthogonalityallocation rule for discriminating the layers, is applied to set the CSparameter values of the other layers (step S737).

In the case of a CS value included in group B shown in Table 9, theuniform scheme, which is an orthogonality allocation rule fordiscriminating UEs other than layers, is applied as the orthogonalityallocation rule, so that the same value as the OCC value of the firstlayer is obtained as the OCC values of the other layers (step S739).Thereafter, the process of generating a reference signal sequence byapplying the CS value and the OCC to the layers and transmitting the RSsequence to the eNodeB is the same as steps S745, S750, S755, and S760in FIG. 7, so a detailed description of the same steps will be omittedhere.

FIG. 10 is a flowchart illustrating a process in which a UE in anMU-MIMO environment calculates an OCC value by selecting anorthogonality allocation rule from control information transmitted froman eNodeB according to an exemplary embodiment.

FIG. 10 shows a process of selecting a CS parameter in linkage group B-1and B-2 used in the case of MU-MIMO among the linkage groups shown inTable 7.

In FIG. 10, steps S1015, S1050, and S1055 are different fromcorresponding steps of FIG. 8 while the other steps are similar to thecorresponding steps of FIG. 8.

In the process shown in FIG. 10, the eNodeB 809 sets a 3 bits CSparameter and transmits control information including the CS parameterto UE #1 801 belonging to the first UE group and UE #2 802 belonging tothe second UE group. Each of the first and second UE groups may includeone or more UEs. The description with reference to FIG. 10 is based onan assumption that each of the UE groups corresponds to one UE. In thisevent, the OCC value can be obtained from the CS parameter by the UEs801 and 802 without separate signaling. Further, the UE can discriminatethe orthogonality allocation rule through the sequence hopping. Thedescription about FIG. 10 is based on the MU-MIMO environment, which isthus limited to the linkage group B-1/B-2. As a result, theorthogonality allocation rule may be limited to the uniform scheme.

The eNodeB 809 generates a control signal, which includes DCI format 0including a 3 bits CS parameter for n_(DMRS) ⁽²⁾ determined for each UEby a higher signaling layer of the system (step S1016). Specifically,the higher signaling layer determines whether each UE to be scheduledwill operate in an SU-MIMO state or an MU-MIMO state. If the UE willoperate in the MU-MIMO state, the eNodeB 809 transmits CS parameter forn_(DMRS) ⁽²⁾ belonging to different CS-OCC linkage groups (groups B-1and B-2 of Table 9) to the UEs (step S1016). Thus, the CS valueallocation is performed to enable the UEs to obtain different OCCvalues.

After steps S818 to S845, each of UE #1 and UE #2 may obtain the OCCvalue from the received CS value based on the linkage group as shown inTable 9. Further, they determine whether the linkage group forcalculation of the OCC value is group A, B-1, or B-2. If the group isgroup B-1 or B-2, each of the UEs employs the uniform scheme as theorthogonality allocation rule and sets the same OCC value for the otherlayers (steps S1050 and S1055). As a result, each of UE #1 801 and UE #2802 can have different OCC values, through which they can be identified.

Thereafter, the process of generating a reference signal sequence byapplying the CS value and the OCC to the layers and transmitting the RSsequence to the eNodeB is similar to the steps S860 to S895 in FIG. 8.

Table 8 shows an example of CS parameter values and OCC indexes selectedaccording to an orthogonality allocation rule proper for the SU-MIMOenvironment or MU-MIMO environment without separate signaling in a statein which the UE cannot determine whether the UE is in the SU-MIMO stateor MU-MIMO state, as shown in FIGS. 7 to 10.

TABLE 8 1^(st) 2^(nd) 3^(rd) 4^(th) UL DM-RS layer layer layer layerSU-MIMO Case 1 - 2 Rank, 1 UE UE A n_(DMRS) ⁽²⁾ 0 6 n_(DMRS) ^(OCC) [+1,+1] [+1, −1] Case 2 - 3 Rank, 1 UE UE A n_(DMRS) ⁽²⁾ 0 4 8 n_(DMRS)^(OCC) [+1, +1] [+1, −1] [+1, +1] Case 3 - 4 Rank, 1 UE UE A n_(DMRS)⁽²⁾ 0 3 6 9 n_(DMRS) ^(OCC) [+1, +1] [+1, −1] [+1, +1] [+1, −1] MU-MIMOCase 4 - 4 Rank per UE A n_(DMRS) ⁽²⁾ 4 7 10  1 UE, 2 UEs n_(DMRS)^(OCC) [+1, +1] [+1, +1] [+1, +1] [+1, +1] UE B n_(DMRS) ⁽²⁾ 8 11  2 5n_(DMRS) ^(OCC) [+1, −1] [+1, −1] [+1, −1] [+1, −1]

In the case of MU-MIMO, UE A has [+1, +1], which is the same OCC for allthe layers, and UE B has [+1, −1], which is the same OCC for all thelayers.

FIG. 11 is a block diagram of an apparatus for transmitting a CSparameter which indicate information relating to the orthogonalityaccording to an exemplary embodiment.

The apparatus shown in FIG. 11 may be an eNodeB.

The apparatus or eNodeB shown in FIG. 11 includes a UE configurationstate determining unit 1110, an orthogonality allocation ruledetermining unit 1120, a CS parameter determining unit 1130, a signalgenerating unit 1150, and a Transmitting/Receiving unit 1160. Theapparatus may further include a CS orthogonality mapping unit 1140.

The UE configuration state determining unit 1110 determines the multipleaccess state of one or more UEs. Thus, the UE configuration statedetermining unit 1110 determines whether a UE operates in an SU-MIMOstate or an MU-MIMO state.

The orthogonality allocation rule determining unit 1120 determines anorthogonality allocation rule according to the determined multipleaccess state of the UE. The orthogonality allocation rule determiningunit 1120 may determine the orthogonality allocation rule to be selectedaccording to the hopping scheme for the reference signal sequence, andthus determine the orthogonality allocation rule selected based on thehopping scheme determined by the UE. Further, the orthogonalityallocation rule determining unit 1120 may determine the orthogonalityallocation rule which the UE may obtain from the CS parameter value asin the embodiment shown in Table 7.

The CS parameter determining unit 1130 determines a CS parameter, bywhich it is possible to calculate the determined orthogonalityallocation rule and orthogonality-related information according to thedetermined multiple access state of the UE.

The signal generating unit 1150 generates a signal for transmittingcontrol information including the determined CS parameter, and theTransmitting/Receiving unit 1160 transmits the signal to the UE.

The CS parameter determining unit 1130 may determine a cyclic shiftparameter, by which it is possible to calculate the determinedorthogonality allocation rule and orthogonality-related informationaccording to the determined multiple access state of the UE.

By applying the embodiment shown in FIGS. 7 and 8, the UE can identifythe orthogonality allocation rule through the sequence hopping scheme.If the multiple access state of the UE is the SU-MIMO state, the UEconfiguration state determining unit 1110 may select a CS from all theCSs that may be allocated. This case includes the example describedabove with reference to FIG. 7. If the UE configuration statedetermining unit 1110 has determined that the multiple access sate ofthe UE is the MU-MIMO state and the UEs include a first UE and a secondUE, CS parameters included in different groups may be selected to obtaindifferent orthogonality-related indicators in allocation of the CSparameters as shown in FIG. 8.

The UE configuration state determining unit 1110 may determine the firstCS parameter to be received by the first UE and the second CS parameterto be received by the second UE, and make first information relating tothe orthogonality calculated from the first CS parameter be differentfrom second information relating to the orthogonality calculated fromthe second CS parameter.

In the case of applying the embodiment shown in FIGS. 9 and 10, the UEcan identify the orthogonality-related information and the orthogonalityallocation rule by using linkage group as shown in Table 7. If themultiple access state of the UE is the SU-MIMO state, the UEconfiguration state determining unit 1110 may select a CS parameter fromamong all CS parameters that may be allocated to the UE in the SU-MIMOstate, such as group A of Table 7. This case includes the exampledescribed above with reference to FIG. 9. If the UE configuration statedetermining unit 1110 has determined that the multiple access state ofthe UE is the MU-MIMO state and the UEs include a first UE and a secondUE, CS parameters included in different groups, such as groups B-1 andB-2 of Table 7, may be selected to enable the UE to obtain differentorthogonality-related indicators in allocation of the CS parameters asshown in FIG. 10 and select an orthogonality allocation rule differentfrom that of group A.

Referring to FIG. 11, the CS parameter may indicate CS parameter valuen_(DMRS) ⁽²⁾ and orthogonality-related information may include an OCCindex. Therefore, CS-OCC linkage groups as shown in Table 5 and Table 7may be used. This information may be stored in the CS orthogonalitymapping unit 1140. Specifically, the CS orthogonality mapping unit 1140divides all CS parameters allocable to the UE into a first set and asecond set as shown in Table 5 or into a 1^(st) set, a 2-1^(st) set, anda 2-2^(nd) set as shown in Table 7, wherein each of intersections of thesets is an empty set, so as to make it possible to obtain theorthogonality-related information through the CS parameter. Of course,as in Table 7, it is possible to obtain the orthogonality allocationrule.

If the bandwidth allocated to the first UE is different from thebandwidth allocated to the second UE, the CS parameters may be set tohave different OCC indexes.

Further, the signal generating unit 1150 generates a signal fortransmitting control information including the determined CS parameterto the UE. The control information may be DCI format 0 included in aPDCCH. Further, the Transmitting/Receiving unit 1160 transmits thegenerated signal to the UE.

The apparatus shown in FIG. 11 includes CS parameter for n_(DMRS) ⁽²⁾ inthe DCI format 0 for transmission, so that each UE not only can obtainorthogonal OCC index but can also determine the scheme for allocatingthe OCC index to each layer, from the CS parameter for n_(DMRS) ⁽²⁾.Therefore, as in the embodiments shown in FIGS. 7 and 8, values that canbe set as the CS parameter for n_(DMRS) ⁽²⁾ are divided into two groups,and an OCC index of 0 is allocated to the CS parameter for n_(DMRS) ⁽²⁾of one group while an OCC index of 1 is allocated to the CS parameterfor n_(DMRS) ⁽²⁾ of the other group. Further, as in the embodimentsshown in FIGS. 9 and 10, those values may be divided into three groups,so as to allow selection of an orthogonality allocation rule. As aresult, even without separate transmission of the OCC index and theorthogonality allocation rule, the UE can obtain the OCC index from thereceived CS parameter for n_(DMRS) ⁽²⁾ and can generate a referencesignal, such as DM-RS, by calculating the CS and the OCC for each layerby applying the orthogonality allocation rule.

Further, the CS parameter may be transmitted through signaling of aphysical layer (L1), such as PDCCH, signaling of a wireless access layeror Medium Access Control (MAC) layer (L2), a Radio Resource Control(RRC) signaling, or L3 signaling such as a message. However, the presentinvention is not limited to such signaling, and the OCC index may be setto have three or more values beyond 0 and 1.

According to the embodiments of the present invention described above,in transmitting a reference signal, such as an uplink DM-RS, inconsideration of each eNodeB (or cell) or each UE in a new environment,such as MU-MIMO or CoMP environment, and increasing antennas in theLTE-A, it is possible to increase the number of orthogonal resources tobe orthogonally multiplexed and thus possible to satisfy theorthogonality by transmitting the parameter value for setting the CSvalue (α) of the DM-RS without change, without separately transmittingorthogonality-related information. Therefore, it is possible to use thebasic CS parameters of the existing LTE while maintaining the backwardcompatibility. Especially, since the OCC have different functionsaccording to whether the UE is in the SU-MIMO state or the MU-MIMOstate, the OCC may be allocated in accordance with the accessenvironment of each network, which can guarantee the orthogonalitybetween reference signal sequences and reduce the interference betweenthem.

FIG. 12 is a block diagram of an apparatus for receiving a CS parameterwhich indicate information relating to the orthogonality andtransmitting a reference signal generated with the information relatingto the orthogonality according to an exemplary embodiment.

The apparatus shown in FIG. 12 may be a UE.

The apparatus or UE shown in FIG. 12 includes a receiving unit 1210, aCS parameter extracting unit 1220, an orthogonality-related informationcalculating unit 1230, an orthogonality allocation rule selecting unit1240, a layer-based information calculating unit 1250, a referencesignal generating unit 1260, and a transmitting unit 1270.

The receiving unit 1210 receives control information from an eNodeB ormay receive a wireless signal including control information from theeNodeB. The control information may be carried by a PDCCH.

The CS parameter extracting unit 1220 extracts a CS parameter for afirst layer from the control signal received by the receiving unit 1210.If the control information is carried by the PDCCH, the CS parameter forn_(DMRS) ⁽²⁾ may be included as a CS parameter in the DCI format 0.

The orthogonality-related information calculating unit 1230 calculatesthe orthogonality-related information for the first layer from the CSparameter for the first layer. This information may be calculated byusing a mapping relation or a predetermined function relating to the CSparameter for the first layer. The orthogonality-related information forthe first layer may be an OCC index indicating an OCC.

For example, if the received CS parameter for the first layer belongs toa particular CS parameter group, such as CS-OCC linkage group, theorthogonality-related information can be calculated from an OCC indexrelating to the particular CS parameter group. Therefore, if one OCC ismapped to one CS parameter group including multiple CS parameters, theOCC can be calculated from all the CS parameters included in the group,as described above in relation to the CS-OCC linkage group shown inTable 5 or 9.

The orthogonality allocation rule selecting unit 1240 selects anorthogonality allocation rule to be used for calculation oforthogonality-related information of the other layers. Specifically, asshown in FIGS. 7 and 8, if a determined current hopping sequencecorresponds to a hopping scheme by the unit of slot, the orthogonalityallocation rule selecting unit 1240 selects an orthogonality allocationrule, which indicates application of the alternating scheme or thedivision scheme to the other layers so as to obtainorthogonality-related information from the orthogonality-relatedinformation of the first layer. Further, if current hopping sequencedoes not correspond to the hopping scheme by the unit of slot, theorthogonality allocation rule selecting unit 1240 may select anorthogonality allocation rule, which indicates application of theuniform scheme to the other layers in order to obtain theorthogonality-related information.

The orthogonality allocation rule may be selected by determining thegroup to which the CS parameter value belongs, by referring to FIGS. 9and 10 and Table 7.

The layer-based information calculating unit 1250 calculates a CSparameter for a K^(th) layer from the CS parameter for the first layer,and obtains orthogonality-related information for the K^(th) layer byapplying the selected orthogonality allocation rule to theorthogonality-related information for the first layer, wherein Nindicates the number of all layers allocated to each UE, K is a numberto indicate the K^(th) layer among a total of N layers, and N is anatural number equal to or larger than 1.

That is, CS parameters for the other layers from the second layer may becalculated in order to reduce the interference according to the numberof layers used by the UE. Further, the orthogonality-related informationmay also be calculated for each layer based on the first layer.

After the information necessary for generation of the reference signalsis obtained, the reference signal generating unit 1260 generates areference signal, an example of which is a DM-RS. More specifically, thereference signal generating unit 1260 generates a reference signal forthe first layer by using orthogonality-related information for the firstlayer and a CS parameter for the first layer, and generates a referencesignal for the K^(th) layer by using orthogonality-related informationfor the K^(th) layer and a CS parameter for the K^(th) layer, in which Nindicates the number of all layers allocated to each UE, K is a numberto indicate the K^(th) layer among a total of N layers, and N is anatural number equal to or larger than 1.

According to an embodiment of the present invention, the referencesignal may be calculated from the base sequence, OCC, CS for each layer,etc. as in Equations 1 and 2.

The reference signal generating unit 1260 calculates CS α by applyingthe) received CS parameters n_(DMRS) ⁽²⁾, n_(DMRS) ⁽¹⁾, andn_(PRS)(n_(s)) for each layer to Equation 2, calculates the basesequence r _(u,v)(n), and generates a DM-RS sequence of each layer byusing Equation 1. Then, the reference signal generating unit 1260multiplies the generated DM-RS sequence by a orthogonal sequence value(+1 or −1) in the OCC index determined for each layer, so as to generatea final DM-RS sequence. Then, the generated DM-RS sequence is mapped toa corresponding symbol of each slot by an RE mapping unit. If themapping has been completed, an SC-FDMA generating unit generates anSC-FDMA symbol from an RE, to which the DM-RS sequence has been mapped.

Therefore, the reference signal generating unit 1260 either may beindependently implemented or may be implemented together with aScrambler, a modulation mapping unit), a transform precoder, a resourceelement mapping unit, and an Single-Carrier FDMA (SC-FDMA) signalgenerating unit, which are elements of a conventional UE.

The generated reference signal is transmitted to an eNodeB by thetransmitting unit 1270.

If the UE is in the SU-MIMO state, the construction shown in FIG. 12 cangenerate a UL DM-RS from the OCC value and CS parameter, so as to reducethe inter-layer interference as much as possible. Further, even if theUE is in the MU-MIMO state, the construction can generate a UL DM-RSfrom the OCC value and CS parameter, so as to reduce the inter-layerinterference and the inter-UE interference as much as possible. Sincethe CS parameter provides an orthogonality allocation rule andinformation on the OCC for maintaining the orthogonality to UEs, it ispossible to guarantee the orthogonality for a UE in the SU-MIMOenvironment through different OCCs between layers of the UE and toguarantee the orthogonality for a UE in the MU-MIMO environment throughdifferent OCCs between UEs. Further, since separate signaling is notgiven to the UEs, the compatibility condition is also satisfied.

The reference signal generating unit 1260 described above may beimplemented either within or in cooperation with an SC-FDMA signalgenerating unit.

Further, the apparatus according to the embodiments shown in FIGS. 7, 8,9, and 10 may additionally include an antenna number determining unitfor determining the number of antennas (or the number of necessarytransmission layers) beyond the configuration shown in FIG. 12. In thisevent, the reference signal generating unit 1260 may generate a DM-RSsequence for each antenna (or layer).

The present disclosure provides a method and an apparatus for allocatingan OCC and a CS value in each layer of a UL DM-RS. If a CS parameter forthe first layer scheduled and determined by a higher signaling layer isgiven (i.e. signaled) to the UE through an eNodeB, the apparatus canallocate an OCC of each layer according to a predetermined orthogonalityallocation rule and a CS value of another layer based on the given orsignaled value. Especially, according to whether the access state of theUE is the SU-MIMO state or the MU-MIMO state, the method and apparatususe different CS values and OCC values and apply different orthogonalityallocation rules for OCC allocation to each layer. The OCC identifieseach layer in the SU-MIMO state and identifies each UE in the MU-MIMOenvironment. Moreover, the orthogonality allocation rule enables ULDM-RS transmission for multiple layers in the LTE-A system, etc. withoutadditional signaling of additional information.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of generating reference signals by aUser Equipment (UE), the method comprising: receiving a Cyclic Shift(CS) parameter from a network; generating the reference signals for Nlayers based on the CS parameter and an Orthogonal Cover Code (OCC), Nbeing an integer; and transmitting the generated reference signals tothe network, wherein the CS parameter is associated with a first set ora second set, an intersection of the first set and the second set is anempty set, and an OCC of a first layer is equal to an OCC of a secondlayer while OCCs of a third layer and a fourth layer are different fromthe OCC of the first layer if the CS parameter is an element of thefirst set, and one OCC is identically allocated to all of the N layersif the CS parameter is an element of the second set.
 2. The method ofclaim 1, wherein the first set is {0, 3, 6, 9}, and elements of thefirst set are allocated to the first layer, the second layer, the thirdlayer, and the fourth layer, respectively.
 3. The method of claim 1,wherein the second set is {1, 4, 7, 10}, and elements of the second setare allocated to the first layer, the second layer, the third layer, andthe fourth layer, respectively.
 4. The method of claim 1, wherein thesecond set is {2, 5, 8, 11}, and elements of the second set areallocated to the first layer, the second layer, the third layer, and thefourth layer, respectively.
 5. The method of claim 1, wherein the CSparameter is a 3-bit value indicating one set from among a plurality ofsets comprising the first set and the second set.
 6. The method of claim5, wherein the 3-bit value further indicates one or more OCCs to beassociated with the N layers.
 7. A User Equipment (UE) to generatereference signals for N layers, the UE comprising: a receiver to receivea Cyclic Shift (CS) parameter from a network a reference signalgenerator to generate the reference signals for N layers based on the CSparameter and an Orthogonal Cover Code (OCC), N being an integer; and atransmitter to transmit the generated reference signals to the network,wherein the CS parameter is associated with a first set or a second set,an intersection of the first set and the second set is an empty set, andan OCC of a first layer is equal to an OCC of a second layer while OCCsof a third layer and a fourth layer are different from the OCC of thefirst layer if the CS parameter is an element of the first set, and oneOCC is identically allocated to all of the N layers if the CS parameteris an element of the second set.
 8. The UE of claim 7, wherein the firstset is {0, 3, 6, 9}, and elements of the first set are allocated to thefirst layer, the second layer, the third layer, and the fourth layer,respectively.
 9. The UE of claim 7, wherein the second set is {1, 4, 7,10}, and elements of the second set are allocated to the first layer,the second layer, the third layer, and the fourth layer, respectively.10. The UE of claim 7, wherein the second set is {2, 5, 8, 11}, andelements of the second set are allocated to the first layer, the secondlayer, the third layer, and the fourth layer, respectively.
 11. The UEof claim 7, wherein the CS parameter is a 3-bit value indicating one setfrom among a plurality of sets comprising the first set and the secondset.
 12. The UE of claim 11, wherein the 3-bit value further indicatesone or more OCCs to be associated with the N layers.
 13. A method ofreceiving reference signals for N layers by a network, the methodcomprising: transmitting a Cyclic Shift (CS) parameter to a UserEquipment (UE), the CS parameter being associated with the referencesignals for N layers, N being an integer; receiving the referencesignals for N layers generated based on the CS parameter and anOrthogonal Cover Code (OCC); and decoding the received referencesignals, wherein the CS parameter is associated with a first set or asecond set, an intersection of the first set and the second set is anempty set, and an OCC of a first layer is equal to an OCC of a secondlayer while OCCs of a third layer and a fourth layer are different fromthe OCC of the first layer if the CS parameter is an element of thefirst set, and one OCC is identically allocated to all of the N layersif the CS parameter is an element of the second set.
 14. The method ofclaim 13, wherein the first set is {0, 3, 6, 9}, and elements of thefirst set are allocated to the first layer, the second layer, the thirdlayer, and the fourth layer, respectively.
 15. The method of claim 13,wherein the second set is {1, 4, 7, 10}, and elements of the second setare allocated to the first layer, the second layer, the third layer, andthe fourth layer, respectively.
 16. The method of claim 13, wherein thesecond set is {2, 5, 8, 11}, and elements of the second set areallocated to the first layer, the second layer, the third layer, and thefourth layer, respectively.
 17. The method of claim 13, wherein the CSparameter is a 3-bit value indicating one set from among a plurality ofsets comprising the first set and the second set.
 18. The method ofclaim 17, wherein the 3-bit value further indicates one or more OCCs tobe associated with the N layers.